Light guide unit, image display device, and display apparatus

ABSTRACT

An image display device includes an image forming unit and a light guide unit. The light guide unit includes a light guide plate and a housing member. The light guide plate is configured to guide light of an image formed in the image forming unit. The housing member is configured to house the light guide plate. The housing member includes a first cover member, a second cover member, and an attachment member. The second cover member is attached to the first cover member. The attachment member is configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority Patent Application JP 2014-062234 filed Mar. 25, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a display apparatus, and more specifically, to a display apparatus for use as a head mounted display (HMD), for example, and also to an image display device suitable for use in the display apparatus, and a light guide unit suitable for use in the image display device.

Japanese Patent Application Laid-Open No. 2006-162767 describes a virtual image display device (image display device), for example. This virtual image display device is well known to provide two-dimensional (2D) images as enlarged virtual images by a virtual-image optical system. The 2D images are those formed by an image forming unit and provided to be viewed by viewers.

This image display device 1100 includes, as shown in the conceptual view of FIG. 43, an image forming unit 111, a collimator optical system 112, and a light guide section 120. The image forming unit 111 includes a plurality of pixels that are arranged in a 2D matrix. The collimator optical system 112 collimates light coming from each of the pixels in the image forming unit 111. The light guide section 120 guides and emits the resulting collimated light coming from the collimator optical system 112. The light emitted from the light guide section 120 is then guided to eyes 21 of a viewer 20. The light guide section 120 is configured by a light guide plate 121, and first and second deflection sections 130 and 140. The light guide plate 121 propagates therein the incoming light by total reflection, and then emits the light. The first deflection section 130 is a single-layer light reflection film, for example, and reflects the light input to the light guide plate 121 so as to achieve total reflection therein. The second deflection section 140 is a multi-layer light reflection film in the multi-layer film structure, for example, and emits the light from the light guide plate 121 after the light is propagated therein by total reflection. If such an image display device 1100 configures an HMD, for example, the resulting display apparatus may be reduced in weight and size.

As another virtual image display device, for example, Japanese Patent Application Laid-Open No. 2007-094175 describes a virtual image display device (image display device) using a holographic diffraction grating. The virtual image display device is well known to provide 2D images as enlarged virtual images by a virtual-image optical system, those 2D images being formed by an image forming unit and provided to be viewed by viewers.

This image display device 1300 basically includes, as shown in the conceptual view of FIG. 44, the image forming unit 111 that displays images, the collimator optical system 112, and a light guide section 320. In the light guide section 320, light coming from the image forming unit 111 is guided to the eyes 21 of the viewer 20. Such a light guide section 320 includes a light guide plate 321, and first and second diffraction grating members 330 and 340. The first and second diffraction grating members 330 and 340 are each a reflective volumetric holographic diffraction grating provided to the light guide plate 321. Collimated light from the collimator optical system 112 enters a first plane 322 of the light guide plate 321, and then is emitted from the first plane 322. The light guide plate 321 has a second plane 323, which is parallel to the first plane 322 thereof. The second plane 323 is provided with the first and second diffraction grating members 330 and 340.

SUMMARY

Such image display devices as described above have problems such as a pixel displacement in images or deformed images to be viewed by a viewer, due to warpage of a light guide plate or deviation of light caused by the light being guided. The warpage and the deviation are caused by a temperature difference between the outside air and the viewer's body or a transient temperature difference when the viewer moves in/out from a room, for example, when the light guide plate is exposed to the outside air.

So, it is thus desirable to provide a light guide unit having a configuration or a structure to hardly cause problems such as warpage of a light guide plate, which results from a difference in temperature of surrounding environments and the like, and to provide an image display device including such a light guide unit, and a display apparatus including such an image display device.

According to an embodiment of the present disclosure, there is provided a light guide unit including a light guide plate, and a housing member configured to house the light guide plate. The housing member includes a first cover member, a second cover member attached to the first cover member, and an attachment member configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member.

According to another embodiment of the present disclosure, there is provided an image display device including an image forming unit, and a light guide unit. The light guide unit includes a light guide plate and a housing member. The light guide plate is configured to guide light of an image formed in the image forming unit. The housing member is configured to house the light guide plate. The housing member includes a first cover member, a second cover member attached to the first cover member, and an attachment member configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member.

According to another embodiment of the present disclosure, there is provided a display apparatus including a frame configured to be mounted on a viewer's head portion, and an image display device attached to the frame. The image display device includes an image forming unit, and a light guide unit. The light guide unit includes a light guide plate and a housing member. The light guide plate is configured to guide light of an image formed in the image forming unit. The housing member is configured to house the light guide plate. The housing member includes a first cover member, a second cover member attached to the first cover member, and an attachment member configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member.

In the light guide unit, the image display device, and the display apparatus according to the embodiments of the present disclosure, the housing member includes the first cover member, the second cover member, and the attachment member, and the light guide plate is attached in the housing member via the attachment member. Thus, this hardly causes problems such as warpage of the light guide plate, which results from a difference in temperature of surrounding environments and the like. It should be noted that the effects described in this specification are merely exemplary ones and not restrictive ones. Further, additional effects may be produced.

These and other objects, features and advantages of the present disclosure will become more apparent in light of the following detailed description of best mode embodiments thereof, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual view of an image display device in a display apparatus in Embodiment 1;

FIG. 2 is a schematic top view of the display apparatus in Embodiment 1 and the like;

FIG. 3A is a schematic side view of the display apparatus in Embodiment 1, and FIG. 3B is a diagram schematically showing propagation of light in a light guide plate in the image display device;

FIG. 4 is a conceptual view of an image display device in a display apparatus in Embodiment 2;

FIG. 5 is a conceptual view of an image display device in a display apparatus in Embodiment 3;

FIG. 6 is a schematic cross-sectional view of a partially-enlarged reflective volumetric holographic diffraction grating in the display apparatus in Embodiment 3;

FIG. 7 is a conceptual view of an image display device in a display apparatus in Embodiment 4;

FIG. 8 is a conceptual view of an image display device in a display apparatus in Embodiment 5;

FIG. 9 is a conceptual view of a modification of the image display device in the display apparatus in Embodiment 5;

FIG. 10 is a conceptual view of another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 11 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 12 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 13 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 14 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 15 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 16 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 17 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 18 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 19 is a conceptual view of still another modification of the image display device in the display apparatus in Embodiment 5;

FIG. 20 is a conceptual view of an image display device in a display apparatus in Embodiment 6;

FIGS. 21A and 21B are each a schematic cross-sectional view of a dimmer unit, schematically showing how the dimmer unit operates in the display apparatus in Embodiment 6;

FIG. 22A is a schematic top view of a display apparatus in Embodiment 7, and FIG. 22B is a schematic view of a circuit that controls an illumination sensor;

FIG. 23A is a schematic top view of a display apparatus in Embodiment 8, and FIG. 23B is a schematic view of a circuit that controls an illumination sensor;

FIG. 24 is a conceptual view of an image display device in a display apparatus in Embodiment 9;

FIG. 25 is a schematic top view of the display apparatus in Embodiment 9;

FIG. 26 is a conceptual view of an image display device in a display apparatus in Embodiment 10;

FIG. 27 is a conceptual view of an image display device in a display apparatus in Embodiment 11;

FIG. 28 is a conceptual view of a modification of the image display device in the display apparatus in Embodiment 11;

FIG. 29 is a conceptual view of an image display device in a display apparatus in Embodiment 12;

FIG. 30 is a conceptual view of an image display device in a display apparatus in Embodiment 13;

FIG. 31 is a schematic front view of a display apparatus in Embodiment 14;

FIG. 32 is another schematic front view of the display apparatus in Embodiment 14, i.e., the display apparatus with no frame;

FIG. 33 is a schematic top view of the display apparatus in Embodiment 14;

FIG. 34 is a top view of the display apparatus in Embodiment 14 when the display apparatus is mounted on a viewer's head portion (only an image display device is shown, and no frame is shown);

FIG. 35 is a schematic front view of a display apparatus in Embodiment 15;

FIG. 36 is another schematic front view of the display apparatus in Embodiment 15, i.e., the display apparatus with no frame;

FIG. 37 is a schematic top view of the display apparatus in Embodiment 15;

FIG. 38 is a conceptual view of a modification of an image forming unit;

FIG. 39 is a conceptual view of another modification of the image forming unit;

FIG. 40 is a conceptual view of still another modification of the image forming unit;

FIG. 41 is a conceptual view of still another modification of the image forming unit;

FIG. 42 is a conceptual view of still another modification of the image forming unit;

FIG. 43 is a conceptual view of a previous image display device; and

FIG. 44 is a conceptual view of another previous image display device in a different configuration from the image display device of FIG. 38.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, Embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not restricted to Embodiments, and various numeric values and materials in Embodiments are illustrative and not restrictive. The description is given in the following order.

1. Description about Light Guide Unit, Image Display Device, and Display Apparatus According to Embodiments of Present Disclosure, and Overall Description

2. Embodiment 1 (Light Guide Unit, Image Display Device, and Display Apparatus According to Embodiments of Present Disclosure)

3. Embodiment 2 (Modification of Embodiment 1)

4. Embodiment 3 (Another Modification of Embodiment 1)

5. Embodiment 4 (Modification of Embodiment 3)

6. Embodiment 5 (Modification of Housing Member in Embodiments 1 to 4)

7. Embodiment 6 (Modification of Embodiments 1 to 5)

8. Embodiment 7 (Modification of Embodiment 6)

9. Embodiment 8 (Another Modification of Embodiment 6)

10. Embodiment 9 (Modification of Embodiments 1 to 8)

11. Embodiment 10 (Modification of Embodiment 9)

12. Embodiment 11 (Another Modification of Embodiment 9)

13. Embodiment 12 (Modification of Embodiments 6 to 11)

14. Embodiment 13 (Modification of Embodiments 6 to 12)

15. Embodiment 14 (Modification of Embodiments 1 to 13)

16. Embodiment 15 (Modification of Embodiment 14), and Others

Description about Light Guide Unit, Image Display Device, and Display Apparatus According to Embodiments of Present Disclosure, and Overall Description

Hereinafter, a light guide unit according to an embodiment of the present disclosure, a light guide unit in an image display device according to an embodiment of the present disclosure, and a light guide unit in a display apparatus according to an embodiment of the present disclosure are collectively referred to as “light guide unit or the like according to an embodiment of the present disclosure”. Either of a first cover member or a second cover member may be positioned on the viewer's side, but in the following description, for convenience, it is assumed that the first cover member is positioned on the viewer's side, and the second cover member is positioned on the outer side in relation to the first cover member (on the side to which outside light is input). The first cover member and the second cover member are bonded to each other via a protrusion formed on an outer edge portion of the first cover member, for example. Alternatively, the first cover member and the second cover member are bonded to each other via a protrusion formed on an outer edge portion of the second cover member. Alternatively, the first cover member and the second cover member are fixed to each other by a frame member. The frame member is disposed on the outer edge portions of the first cover member and the second cover member and bonded to the outer edge portions of the first cover member and the second cover member. It should be noted that in the following description, the protrusion formed on the outer edge portion of the first cover member, the protrusion formed on the outer edge portion of the second cover member, and the frame member are collectively sometimes referred to as “support unit”.

The attachment member may attach a light guide plate to a housing unit while being in contact with the entre outer circumferential portion of the light guide plate, may attach the light guide plate to the housing unit while being in contact with the outer circumferential portion of the light guide plate at one spot (one area), or may attach the light guide plate to the housing unit while being in contact with the outer circumferential portion of the light guide plate at a plurality of spots (a plurality of areas).

In the light guide unit or the like according to an embodiment of the present disclosure, the attachment member may be made of a thermal insulation material. In such a case, the thermal conductivity of the attachment member may be smaller than the thermal conductivity of the light guide plate, the first cover member, and the second cover member.

Examples of the material for the first cover member, the second cover member, and the light guide plate may include, specifically, a transparent glass substrate including soda lime glass and super white glass, an optical glass including quartz glass and BK7, a plastic substrate, a plastic sheet, and a plastic film. Herein, the plastic material is exemplified by polyethylene terephthalate, polyethylene naphthalate, polycarbonate, cellulose ester such as acetylcellulose, fluorinated polymer such as copolymer of polyvinylidene difluoride or polytetrafluoroethylene and hexafluoropropene, polyether such as polyoxymethylene, polyacetal, polystyrene, polyethylene, polypropylene, polyolefin such as methylpentene polymer, polyimide including polyamideimide, or polyetherimide, polyamide, polyethersulfone, polyphenylene sulfide, polyvinylidene difluoride, tetraacetyl cellulose, bromphenoxy, polyarylate, polysulfone, PMMA (polymethyl methacrylate), acrylic resin, cycloolefin polymer (COP) resin, and the like. The plastic sheet and the plastic film may be rigid not to be easily bent, or may be flexible.

Additionally, examples of the material for the attachment member may include resin materials (specifically, epoxy resin, modified silicone resin, epoxy-modified silicone resin, urethane resin, and the like), porous materials (specifically, porous alumina, porous silicon carbide, porous carbon, plastic sintered porous body, and the like), silica aerogel, low refractive index materials (specifically, cycloolefin polymer (COP) resin, silicone resin), and glass materials. Alternatively, examples of the material for the attachment member may include metal materials or alloy materials such as magnesium alloy. As described above, the support unit may be made of the same material as the first cover member or the second cover member. In the case where the support unit is formed from the frame member, the frame member may be made of the same material as the first cover member or the second cover member, or made of the same kind of material as or a different kind of material from the first cover member or the second cover member. Alternatively, the frame member may be made of metal materials and alloy materials such as a magnesium alloy, aluminum, and an aluminum alloy.

Alternatively, in the light guide unit or the like according to an embodiment of the present disclosure, the attachment member may be made of a buffer material. In this case, the attachment member may have an elastic modulus that is smaller than an elastic modulus of the light guide plate. Here, the material for the light guide plate is as described above. Further, examples of the material for the attachment member may also include the resin materials, silica aerogel, glass, and metal materials and alloy materials such as a magnesium alloy.

In the light guide unit or the like according to an embodiment of the present disclosure including various desirable forms described above, the light guide plate may be attached to the first cover member with the attachment member, but it is not restrictive. The light guide plate may be attached to the second cover member with the attachment member or to the support unit with the attachment member.

Furthermore, in the light guide unit or the like according to an embodiment of the present disclosure including various desirable forms described above, a gap may be provided between the light guide plate and the first cover member, and a gap may be provided between the light guide plate and the second cover member. In this case, air may be present in the gaps, and at least one of the cover members may be provided with an opening. Specifically, the first cover member may be provided with an opening, the second cover member may be provided with an opening, or the first cover member and the second cover member may be provided with respective openings. Alternatively, the gaps may be filled with inert gas or may be at reduced pressure.

Alternatively, in the light guide unit or the like according to an embodiment of the present disclosure including various desirable forms described above, a resin layer may be provided between the light guide plate and the first cover member, and a resin layer may be provided between the light guide plate and the second cover member. In this case, it is desirable that the resin layer have a thermal conductivity smaller than the thermal conductivity of the light guide plate, the first cover member, and the second cover member. Examples of the material for the resin layer may include thermosetting resin and ultraviolet curable resin such as epoxy-based resin and acrylic-based resin. It should be noted that the resin layer may be replaced by a layer made of the porous materials, silica aerogel, or low refractive index materials described above.

Moreover, in the various desirable forms and configurations described above, it is desirable that the first cover member and the second cover member be made of a material through which light passes. The material for the first cover member and the second cover member is as described above.

Moreover, in the various desirable forms and configurations described above, an ultraviolet ray protective layer may be provided to an outer surface of the cover member (e.g., specifically to the second cover member) on the side to which outside light is input. Further, it is desirable to provide an antireflective layer to an outer surface of the cover member (e.g., specifically to the first cover member) on the viewer's side, which is opposite to the side to which outside light is input. The material for the ultraviolet ray protective layer and the antireflective layer may be well-known materials.

Moreover, in the various desirable forms and configurations described above, the light guide unit may include a dimmer unit. Specifically, the dimmer unit may be attached to one of the cover members. Alternatively, the dimmer unit may be attached to the image display device or to a frame. In such a manner, providing the dimmer unit may allow the degradation of images to be viewed by a viewer, which is caused by input of outside light, to be prevented or allow high contrast to be provided to images to be viewed by the viewer.

The image display device may include

(A) an image forming unit, and

(B) a light guide unit configured to receive light coming from the image forming unit, guide the light, and emit the light. In this case, the light guide unit may include

(a) a light guide plate configured to propagate therein by total reflection the light provided by the image forming unit, and emit the light, i.e., light guide plate configured to guide the light of an image formed by the image forming unit),

(b) a first deflection section configured to deflect at least part of the light input to the light guide plate to achieve total reflection of the light in the light guide plate, and

(c) a second deflection section configured to deflect the light propagated in the light guide plate by total reflection to emit the light from the light guide plate. Herein, the term of “total reflection” means total reflection or total reflection in the light guide plate. This is also applicable to the below.

The light guide unit may be transmissive or semi-transmissive (see-through type). Specifically, at least a part of the light guide unit facing the eyes of a viewer may be transmissive or semi-transmissive (see-through), and through such a part of the light guide unit, the viewer may see the outside view. The display apparatus according to an embodiment of the present disclosure may include one image display device (monocular type), or two image display devices (binocular type).

In this specification, when the term of “semi-transmissive” is used, it does not mean that one half (50%) of incoming light is passed through or reflected, but means that incoming light is partially passed through and the remaining is reflected.

In such a desirable display apparatus, a desirable image display device, and a desirable light guide unit according to the embodiments of the present disclosure, the first deflection section reflects light input to the light guide unit, and the second deflection section passes through and reflects the light after the light is propagated in the light guide plate by total reflection. In this case, the first deflection section may serve as a reflection mirror, and the second deflection section may serve as a semi-transmissive mirror. For entirely reflecting the light input to the light guide plate, the first deflection section may be made of metal including alloy to serve as a light reflection film (a kind of mirror) that reflects the light input to the light guide plate. For partially reflecting the light input to the light guide plate, the first deflection section may be a multi-layer film structure of a plurality of dielectric layers, a half mirror, or a polarized beam splitter. The first deflection section reflects at least part of the collimated light input to the light guide plate so as to achieve total reflection of the light in the light guide plate. On the other hand, the second deflection section reflects the collimated light for a plurality of times after the light is propagated by total reflection in the light guide plate. The light remains collimated when it is emitted from the light guide plate. The second deflection section may be a multi-layer film structure of a plurality of dielectric layers, a half mirror, a polarized beam splitter, or a holographic diffraction grating film. These first and second deflection sections are both provided in the light guide plate (incorporated in the light guide plate), and the first deflection section reflects the collimated light input to the light guide plate so as to achieve total reflection of the light in the light guide plate. On the other hand, the second deflection section reflects or diffracts the collimated light for a plurality of times after the light is propagated by total reflection in the light guide plate. The light remains collimated when it is emitted from the light guide plate.

Alternatively, the first deflection section may diffract and reflect the light input to the light guide plate, and the second deflection section may diffract and reflect the light for a plurality of times after the light is propagated by total reflection in the light guide plate.

In this case, the first and second deflection sections may be each configured by a diffraction grating element. These diffraction grating elements may be each a reflective diffraction grating element or a transmissive diffraction grating element, or one of the diffraction grating elements may be a reflective diffraction grating element, and the remaining diffraction grating element may be a transmissive diffraction grating element. The reflective diffraction grating element is exemplified by a reflective volumetric holographic diffraction grating. For convenience, the first deflection section being a reflective volumetric holographic diffraction grating is sometimes referred to as “first diffraction grating member”, and the second deflection section being a reflective volumetric holographic diffraction grating is sometimes referred to as “second diffraction grating member”.

The display apparatus according to the embodiment of the present disclosure offers image display in a color, e.g., green. In this case, with the viewing angle divided into two, more specifically, with the viewing angle equally divided into two, for example, the first deflection section for use may be a laminate structure of two diffraction grating members, each of which corresponds to one-half of the viewing angle. When the display apparatus offers color image display, the first and second deflection sections may be each a laminate structure of P diffraction grating members in order to be ready for diffraction and reflection of P types of light in P different wavelength bands (or wavelengths), e.g., P is 3 for red, green, and blue. In this case, the diffraction grating members are each provided with an interference pattern corresponding to one wavelength band (or wavelength). Alternatively, to be ready for diffraction and reflection of P types of light in P different wavelength bands (or wavelengths), one-layer diffraction grating member may be formed with P types of interference patterns. Still alternatively, first to third light guide plates may be stacked together with intervals thereamong. The first light guide plate is provided with a diffraction grating member being a layer of reflective volumetric holographic diffraction grating that diffracts and reflects light in a red wavelength band (or wavelength).

The second light guide plate is provided with a diffraction grating member being a layer of reflective volumetric holographic diffraction grating that diffracts and reflects light in a green wavelength band (or wavelength). The third light guide plate is provided with a diffraction grating member being a layer of reflective volumetric holographic diffraction grating that diffracts and reflects light in a blue wavelength band (or wavelength). Such configurations accordingly increase the diffraction efficiency, increase the angle available for diffraction, and optimize the angle at which diffraction and reflection occur when the light in each wavelength band (or wavelength) is diffracted and reflected in the diffraction grating members.

The first and second diffraction grating members are each made of a photopolymer material. The first and second diffraction grating members each being a reflective volumetric holographic diffraction grating may be the same as a previous reflective volumetric holographic diffraction grating in terms of material and basic configuration. The reflective volumetric holographic diffraction grating means a holographic diffraction grating that diffracts and reflects only +1 order diffracted light. The diffraction grating member is provided with an interference pattern from the inside to the surface thereof, and the interference pattern itself may be formed similarly to a previous interference pattern. As a specific example, a substance to be a diffraction grating member, e.g., photopolymer material, may be exposed to object light from a first predetermined direction on one side, and at the same time, the substance is also exposed to reference light from a second predetermined direction on the other side. Such exposure to the object light and the reference light accordingly forms an interference pattern, and the resulting interference pattern may be recorded inside of the substance. With the appropriately-selected first and second predetermined directions, and with the appropriately-selected wavelengths for the object and reference light, the resulting interference pattern may have a desired pitch and a desired slant angle on the surface of the diffraction grating member. The slant angle of the interference pattern means an angle at which the surface of the diffraction grating member (or the diffraction grating layer) forms with the interference pattern. When the first and second diffraction grating members are each a laminate structure of P diffraction grating layers each being a reflective volumetric holographic diffraction grating, the P diffraction grating layers may be formed separately, and then stacked on (bonded to) one another using a UV (ultraviolet) curing agent, for example. For forming the P diffraction grating layers, alternatively, a diffraction grating layer may be first formed using an adhesive photopolymer material, and for attachment thereon, other diffraction grating layers may be then formed one by one also using an adhesive photopolymer material.

In such a desirable display apparatus according to the embodiment of the present disclosure, the image forming unit may include a plurality of pixels arranged in a 2D matrix. Such an image forming unit may be referred to as “image forming unit having a first configuration” for convenience.

The image forming unit having a first configuration may be configured by a reflective spatial light modulator and a light source, by a transmissive spatial light modulator and a light source, or by a light-emitting element such as light-emitting diode (LED), semiconductor laser element, organic EL (Electro Luminescence) element, or inorganic EL element. The desirable image forming unit is configured by a reflective spatial light modulator and a light source. The spatial light modulator is exemplified by a light valve, for example, a transmissive or reflective liquid crystal display such as LCOS (Liquid Crystal On Silicon), and a digital micro mirror device (DMD). The light source is exemplified by the above-mentioned light-emitting element. The reflective spatial light modulator may include a liquid crystal display and a polarized beam splitter with which light coming from the light source is partially reflected and directed to the liquid crystal display, and the light reflected by the liquid crystal display is partially passed and directed to the optical system. The light-emitting element for the light source may include red, green, blue, and white light emitting elements.

Alternatively, the light emitted from these red, green, and blue light-emitting elements, i.e., red, green, and blue light, may be mixed and made uniform in luminance using a light pipe to obtain white light. Such light-emitting elements may be each a semiconductor laser element, a solid-state laser, or an LED, for example. The number of the pixels may be determined based on the specifications expected for the image display device, and the specific number of the pixels may be 320×240, 432×240, 640×480, 854×480, 1024×768, or 1920×1080, for example. The collimator optical system that will be described later is capable of converting information about pixel position into information about angle of the light guide section in the optical system. The collimator optical system has the positive optical power as a whole and is a convex lens, a concave lens, a free-shaped prism, or a holographic lens, or a combination thereof, for example.

Alternatively, in the display apparatus according to the embodiment of the present disclosure, the image forming unit may include a light source, and a scanning section that scans collimated light coming from the light source. Such an image forming unit may be referred to as “image forming unit having a second configuration” for convenience.

The light source in the image forming unit having a second configuration may be a light-emitting element, specifically including red, green, blue, and white light-emitting elements. Alternatively, the light emitted from these red, green, and blue light-emitting elements, i.e., red, green, and blue light, may be mixed and made uniform in luminance using a light pipe to obtain white light. Such light-emitting elements may be each a semiconductor laser element, a solid-state laser, or an LED, for example. The number of the pixels (virtual pixels) in the image forming unit having a second configuration may also be determined based on the specifications expected for the image display device, and the specific number of the pixels (virtual pixels) may be 320×240, 432×240, 640×480, 854×480, 1024×768, or 1920×1080, for example. When the light source is configured by the red, green, and blue light-emitting elements for color image display, a cross prism is desirably used for color composition, for example. The scanning section scans horizontally and vertically light coming from the light source, and may be a MEMS (Micro Electro Mechanism Systems) including a micro mirror that is rotatable in the 2D direction, or a galvano mirror, for example. A relay optical system that will be described next may be a well-known relay optical system.

In the image forming unit having a first configuration and the image forming unit having a second configuration, the optical system collimates light, and directs the resulting collimated light beams into the light guide plate.

Such an optical system is sometimes referred to as “collimator light emitting optical system”, and is specifically a collimator optical system or a relay optical system. The reason why the light remains collimated is that information about optical wavefront when such light beams are input to the light guide plate is expected to be stored even after the light beams are emitted therefrom via the first and second deflection sections. For generating collimated light beams, a light emitting section of the image forming unit may be positioned at the focal length in the collimator light emitting optical system, for example. The collimator light emitting optical system is capable of converting information about pixel position into information about angle of the light guide unit in the optical system. The collimator light emitting optical system has the positive optical power as a whole, and is a convex lens, a concave lens, a free-shaped prism, or a holographic lens, or a combination thereof, for example.

Alternatively, as the image forming unit or the light source configured by light-emitting elements and a light valve, the following configurations may be also possible other than the combination of a backlight that emits white light as a whole, and a liquid crystal display including red, green, and blue light-emitting pixels.

[Image Forming Unit A]

An image forming unit A may include

(α) a first image forming unit being a first light-emitting panel in which first light-emitting elements are arranged in a 2D matrix, the first light-emitting elements emitting blue light,

(β) a second image forming unit being a second light-emitting panel in which second light-emitting elements are arranged in a 2D matrix, the second light-emitting elements emitting green light,

(γ) a third image forming unit being a third light-emitting panel in which third light-emitting elements are arranged in a 2D matrix, the third light-emitting elements emitting red light, and

(δ) a section configured to collectively direct the light emitted from the first, second, and third image forming units to a single optical path, e.g., this section is a dichroic prism, and this is also applicable to the below.

The image forming unit A controls light-emission/no light-emission of the first, second, and third light-emitting elements.

[Image Forming Unit B]

An image forming unit B includes

(α) a first image forming unit including first light-emitting elements that emit blue light, and a first light-pass control unit configured to control light-pass/no light-pass of light coming from the first blue light-emitting elements, i.e., this first light-pass control unit is a kind of light valve, and may be a liquid crystal display, a digital micro mirror device (DMD), or an LCOS, for example, and this is also applicable to the below,

(β) a second image forming unit including second light-emitting elements that emit green light, and a second light-pass control unit (light valve) configured to control light-pass/no light-pass of light coming from the second green light-emitting elements,

(γ) a third image forming unit including third light-emitting elements that emit red light, and a third light-pass control unit (light valve) configured to control light-pass/no light-pass of light coming from the third red light-emitting elements, and

(δ) a section configured to collectively direct the light passed through the first, second, and third light-pass control units to a single optical path.

Image display is performed by the light-pass control units controlling light-pass/no light-pass of light coming from the light-emitting elements. For guiding the light from the first, second, and third light-emitting elements to the light-pass control units, a section (light directing member) in use may be a light guide member, a micro lens array, a mirror, a reflection plate, or a condenser lens, for example.

[Image Forming Unit C]

An image forming unit C includes

(α) a first image forming unit including a first light-emitting panel, and a blue light-pass control unit (light valve), the first light-emitting panel including first light-emitting elements arranged in a 2D matrix, the first light-emitting elements emitting blue light, the blue light-pass control unit being a unit configured to control light-pass/no light-pass of light coming from the first light-emitting panel,

(β) a second image forming unit including a second light-emitting panel, and a green light-pass control unit (light valve), the second light-emitting panel including second light-emitting elements arranged in a 2D matrix, the second light-emitting elements emitting green light, the green light-pass control unit being a unit configured to control light-pass/no light-pass of light coming from the second light-emitting panel,

(γ) a third image forming unit including a third light-emitting panel, and a red light-pass control unit (light valve), the third light-emitting panel including third light-emitting elements arranged in a 2D matrix, the third light-emitting elements emitting red light, the red light-pass control unit being a unit configured to control light-pass/no light-pass of light coming from the third light-emitting panel, and

(δ) a section configured to collectively direct the light emitted from the blue, green, and red light-pass control units to a single optical path.

Image display is performed by the light-pass control units (light valves) controlling light-pass/no light-pass of light coming from these first, second, and third light-emitting panels.

[Image Forming Unit D]

An image forming unit D is a field-sequential color image forming unit, including

(α) a first image forming unit including first light-emitting elements that emit blue light,

(β) a second image forming unit including second light-emitting elements that emit green light,

(γ) a third image forming unit including third light-emitting elements that emit red light,

(δ) a section configured to collectively direct light emitted from the first, second, and third image forming units to a single optical path, and

(ε) a light-pass control unit (light valve) configured to control light-pass/no light-pass of light emitted from the optical-path-directing section.

Image display is performed by the light-pass control unit controlling light-pass/no light-pass of light coming from these light-emitting elements.

[Image Forming Unit E]

An image forming unit E is also a field-sequential color image forming unit, including

(α) a first image forming unit being a first light-emitting panel including first light-emitting elements arranged in a 2D matrix, the first light-emitting elements emitting blue light,

(β) a second image forming unit being a second light-emitting panel including second light-emitting elements arranged in a 2D matrix, the second light-emitting elements emitting green light,

(γ) a third image forming unit being a third light-emitting panel including third light-emitting elements arranged in a 2D matrix, the third light-emitting elements emitting red light,

(δ) a section configured to collectively direct light emitted from the first, second, and third image forming units to a single optical path, and

(ε) a light-pass control unit (light valve) configured to control light-pass/no light-pass of light emitted from the optical-path-directing section.

Image display is performed by the light-pass control unit controlling light-pass/no light-pass of light coming from these light-emitting panels.

[Image Forming Unit F]

An image forming unit F is a passive- or active-matrix color image forming unit configured to perform image display by controlling light-emission/no light-emission of first, second, and third light-emitting elements.

[Image Forming Unit G]

An image forming unit G is a field-sequential color image forming unit, including a light-pass control unit (light valve) configured to control light-pass/no light-pass of light coming from light-emitting element units arranged in a 2D matrix. Image display is performed by time-sharing control executed over light-emission/no light-emission of first, second, and third light-emitting elements in the light-emitting element units, and by the light-pass control unit controlling light-pass/no light-pass of light coming from first, second, and third light-emitting elements.

In order that the light that is emitted from the image forming unit and input to the light guide plate is not reflected, an opening may be provided to the cover member on the viewer's side (which is opposite to the side to which outside light is input), as described above. Further, in order that the light from a collimator light emitting optical system is not reflected by the cover member, a light shielding layer may be formed in a part of the cover member on the viewer's side or in the circumference of the opening of the cover member, or an antireflective layer may be formed as described above.

Alternatively, when the display apparatus according to the embodiment of the present disclosure is of a binocular type,

the light guide plate is provided to be closer as a whole to the center side of the viewer's face than the image forming units,

a coupling member is further provided to couple the two image display devices,

the coupling member is attached to the center portion of a frame on the side facing the viewer, the frame being positioned between the viewer's two eyes, and

a projection image of the coupling member is in a projection image of the frame.

In such a configuration that the coupling member is attached to the center portion of the frame positioned between the viewer's two eyes, that is, if the image display devices are not directly attached to the frame, temple sections are extended outward when the viewer wears the frame on his head portion. Therefore, even if the frame is deformed, the frame deformation does not cause displacement (position change) of the image forming units or the light guide plate, and even if such displacement occurs, the displacement is negligible. Such a configuration thus prevents a change of convergence angle between right and left images without fail. Further, the configuration eliminates having to increase the rigidity of the front part of the frame so that the frame is not increased in weight, the design ability is not impaired, and the cost is not increased. Still further, with the image display devices not directly attached to the eyeglass-shaped frame, the frame may be in various designs and colors to meet the viewer's preferences, and the frame designing is less restricted and highly flexible. What is more, the coupling member is positioned between the viewer and the frame, and the projection image of the coupling member is in the projection image of the frame, i.e., when the head mounted display is viewed from the front of the viewer, the coupling member is hidden behind the frame. This offers the head mounted display with sophistication and refinement of design.

Herein, desirably, the coupling member is attached to the center portion of a front section on the side facing the viewer. The front section is positioned between the viewer's two eyes, and corresponds to a bridge section of ordinary glasses.

In the state that the coupling member couples together the two image display devices, specifically, the image forming units may be respectively attached to end portions of the coupling member to be adjustable. In this configuration, the image forming units are desirably positioned outside of the viewer's eyes. Such a configuration also desirably satisfies 0.01×L≦α≦0.30×L, or 0.05×L≦α≦0.25×L, 0.35×L≦β≦0.65×L, or 0.45×L≦β≦0.55×L, 0.70×L≦γ≦0.99×L, or 0.75×L≦γ≦0.95×L, where α denotes a distance from the attachment center for one of the image forming units to one end portion (one endpiece) of the frame, β denotes a distance from the center of the coupling member to the one end portion (the one endpiece) of the frame, γ denotes a distance from the attachment center for the remaining image forming unit to the one end portion (the one endpiece) of the frame, and L denotes a length of the frame. For respectively attaching the image forming units to the end portions of the coupling member, specifically, three through holes are formed to each of the end portions of the coupling member, and screw sections corresponding to these through holes are formed to each of the image forming units.

Thereafter, screws are fastened into the screw sections formed to the image forming units through the through holes. Between each of the screws and each of the screw sections, a spring is inserted in advance. Therefore, by controlling the degree of screw fastening, the image forming units may be adjusted in state of attachment, i.e., adjusted in angle with respect to the coupling member.

Herein, the expression of “the attachment center for the image forming unit” denotes a point at which an overlapped portion between the projection image of the image forming unit and the projection image of the frame is divided equally into two along the axis of the frame. The projection images are those obtained by projecting the image forming unit and the frame onto a virtual plane when the image forming unit is attached to the coupling member. The expression of “the center of the coupling member” denotes, when the coupling member is attached to the frame, a point at which a portion where the coupling member is in contact with the frame is divided equally into two along the axis of the frame. The expression of “the length of the frame” means the length of the projection image of the frame when the frame is bent. Note that the projection direction is vertical to the viewer's face.

Alternatively, in the state that the coupling member couples together the two image display devices, specifically, the coupling member may couple together two light guide plates. Note here that the two light guide plates may be integrally manufactured. If this is the case, the coupling member is coupled to the integrally-manufactured light guide plate, and this configuration is also regarded as the coupling member coupling together two light guide plates. When a distance from the center of one of the image forming units to one end portion of the frame is α′, and when a distance from the center of the remaining image forming unit to the end portion of the frame is γ′, the values of α′ and γ′ are desirably similar to those of α and γ described above. The expression of “the center of the image forming unit” denotes a point at which an overlapped portion between the projection image of the image forming unit and the projection image of the frame is divided equally into two along the axis of the frame. The projection images are those obtained by projecting the image forming unit and the frame onto a virtual plane when the image forming unit is attached to the light guide plate.

The shape of the coupling member may be essentially arbitrary as long as the projection image thereof is in the projection image of the frame, e.g., like a rod or a slim plate. The material for the coupling member may be metal, alloy, plastic, or a combination thereof.

A light beam emitted from the center of the image forming unit and passed through a node in the optical system on the side of the image forming unit is referred to as “center light beam”, and a part of the center light beam vertically entering the light guide unit is referred to as “at-center incident light beam”. The point at which the at-center incident light beam enters the light guide unit is referred to as “light-guide-unit center point”. The axis passing through the light-guide-unit center point and being parallel to the axis of the light guide unit is referred to as “X axis”, and the axis passing through the light-guide-unit center point and coinciding with the normal to the light guide unit is referred to as “Z axis”. In the display apparatus according to the embodiment of the present disclosure, the horizontal direction is parallel to the X axis, and hereinafter, may be sometimes referred to as “X-axis direction”. Herein, the optical system is disposed between the image forming unit and the light guide unit, and collimates light coming from the image forming unit. The resulting collimated luminous flux is input to the light guide unit, is guided therein, and is emitted therefrom. The center point of the first deflection section is the “light-guide-unit center point”.

The light guide plate includes two parallel planes (first and second planes) extending parallel to the axis of the light guide plate, i.e., in a longitudinal direction, a horizontal direction, and corresponds to the X axis. The width direction of the light guide plate (height direction, vertical direction) corresponds to the Y axis. When the plane of the light guide plate to which light is input is the light-guide-plate incident plane, and the plane of the light guide plate from which light exits is the light-guide-plate exit plane, the first plane may serve both as the light-guide-plate incident plane and the light-guide-plate exit plane, or the first plane may serve as the light-guide-plate incident plane, and the second plane may serve as the light-guide-plate exit plane. The interference pattern on the diffraction grating member is extended substantially parallel to the Y axis.

In the display apparatus according to the embodiment of the present disclosure, the frame may be configured by a front section, and two temple sections. The front section is disposed to be in front of a viewer, and the temple sections are respectively attached to the ends of the front section via hinges to be able to rotate. The tip end portion of each of the temple sections is provided with a temple tip section. In the state that the image display device is attached to the frame, specifically, the image forming unit may be attached to the temple sections. The front section and the two temple sections may be integrally manufactured. That is, when the display apparatus according to the embodiment is viewed in its entirety, the frame looks substantially the same as that of ordinary glasses. The material for the frame may be the same as that for the ordinary glasses, e.g., metal, alloy, plastic, or a combination thereof. The front section may be provided with a nose pad. That is, when the display apparatus according to the embodiment is viewed in its entirety, the structure of the frame with the nose pad looks substantially the same as that of the ordinary glasses except that there is no rim.

The nose pad may also be in the well-known structure and configuration.

In the display apparatus according to the embodiment of the present disclosure, considering design and ease of attachment, desirably, a wiring line (signal line or power supply line) from one or two image forming units goes through the temple section and the temple tip section to be outside from the tip end portion of the temple tip sections, and then is connected to a control unit (control circuit or control section). The image forming unit may be provided with a headphone section, and if this is the configuration, a headphone-use wiring line from the image forming unit goes through the temple section and the temple tip section to reach the headphone section via the tip end portion of the temple tip section. The headphone section may be of an in-ear type or a canal type, for example. To be more specific, desirably, the headphone-use wiring line goes around behind the pinna from the tip end portion of the temple tip section, and reaches the headphone section.

In the display apparatus according to the embodiment of the present disclosure, an imaging unit may be attached to the center or end portion of the front section, or to the temple sections, for example. A wiring line from the imaging unit may be connected to the image display device (or the image forming unit) via the front section, or may be merged with another wiring line extending from the image display device (or the image forming unit), for example.

When the display apparatus includes a dimmer unit, the dimmer unit includes

first and second substrates, the first substrate opposing the light guide unit, the second substrate opposing the first substrate,

first and second electrodes respectively provided to the first and second substrates, and

a light-transmission control material layer sealed between the first and second substrates.

The first substrate may also be a component in the light guide unit. The display apparatus in such a configuration is referred to as “display apparatus according to a first embodiment of the present disclosure” for convenience. In the display apparatus according to a first embodiment of the present disclosure, with the first substrate in the dimmer unit being also a component in the light guide unit, the entire weight may be reduced so that this does not cause discomfort to a user of the display apparatus. The second substrate may be made thinner than the first substrate. The first substrate in the dimmer unit may serve also as the second cover member, for example.

In the dimmer unit, the light-transmission control material layer may be an optical shutter being a liquid crystal material layer, or may be an optical shutter being an inorganic EL material layer. However, this is not restrictive, and the optical shutter for use in the dimmer unit may also be configured by an electrophoretic dispersion liquid including a large number of electrically-charged electrophoretic particles and a dispersion medium colored differently from the electrophoretic particles, by application of electrodeposition/dissociation that occurs in response to the reversible oxidation reduction of metal, e.g., silver particles, by utilizing color change of substance that occurs in response to the oxidation reduction of an electrochromic material, or by controlling the light transmittance by electrowetting. When the dimmer unit is an optical shutter in which the light-transmission control material layer is a liquid crystal material layer, the material for the light-transmission control material layer may be TN (Twisted Nematic) liquid crystal, or STN (Super Twisted Nematic) liquid crystal, for example, but this is not restrictive. When the dimmer unit is an optical shutter in which the light-transmission control material layer is an inorganic EL material layer, the material for the light-transmission control material layer may be tungsten oxide (WO₃), for example, but this is not restrictive. In the display apparatus according to the embodiment of the present disclosure, desirably, the light guide unit and the dimmer unit are disposed in this order from the viewer's side, but this order may be reversed.

The material of the first and second substrates is specifically exemplified by a transparent glass substrate including soda lime glass and super white glass, a plastic substrate, a plastic sheet, and a plastic film. Herein, the plastic material is exemplified by polyethylene terephthalate, polyethylene naphthalate, polycarbonate, cellulose ester such as acetylcellulose, fluorinated polymer such as copolymer of polyvinylidene difluoride or polytetrafluoroethylene and hexafluoropropene, polyether such as polyoxymethylene, polyacetal, polystyrene, polyethylene, polypropylene, polyolefin such as methylpentene polymer, polyimide including polyamideimide, or polyetherimide, polyamide, polyethersulfone, polyphenylene sulfide, polyvinylidene difluoride, tetraacetyl cellulose, bromphenoxy, polyarylate, polysulfone, or others. The plastic sheet and the plastic film may be rigid not to be easily bent, or may be flexible.

When the first and second substrates are each configured by a transparent plastic substrate, the inner surface of the substrate may be formed with a barrier layer made of an inorganic or organic material.

The first and second substrates are respectively provided with first and second electrodes, e.g., so-called transparent electrodes. The first and second electrodes are each specifically made of indium tin oxide (ITO, including Sn-doped In₂O₃, crystalline ITO, and amorphous ITO), fluorine doped SnO₂ (FTO), IFO (F-doped In₂O₃), antimony doped SnO₂ (ATO), SnO₂, ZnO (including Al-doped ZnO, and B-doped ZnO), indium zinc oxide (IZO), spinel oxide, oxide with YbFe₂O₄ structure, or conductive polymers including polyaniline, polypyrrole, and polythiophene, for example, but these are not restrictive, or a combination of two or more of them is also possible. The first and second electrodes may be each formed by physical vapor deposition (PVD) such as vacuum deposition and sputtering, various types of chemical vapor deposition (CVD), or various types of coating, for example. Patterning of the electrodes may be arbitrarily performed by etching, lifting off, or using various types of masks. In some cases, the patterning of the electrodes is unnecessary.

The first and second substrates are attached together by being sealed at outer edge portions using a sealing agent. The sealing agent for use may be various types of resin including thermosetting resin, light curing resin, moisture curing resin, and anaerobic curing resin, e.g., epoxy resin, urethane resin, acrylic resin, vinyl acetate resin, enethiol resin, silicone resin, and modified polymer resin.

The display apparatus is further provided with an illumination sensor that measures the illumination in the environment where the display apparatus is disposed. Such an illumination sensor is sometimes referred to as “environmental illumination measurement sensor” for convenience. With the illumination sensor (environmental illumination measurement sensor), the measurement result thereof is used as a basis to control the light transmittance of the dimmer unit, or to control the luminance of images to be formed by the image forming unit.

The display apparatus is also further provided with a second illumination sensor that measures the illumination based on the light passed through the dimmer unit from the outside environment. Such a second illumination sensor is sometimes referred to as “transmitted-light illumination measurement sensor” for convenience. With the second illumination sensor (transmitted-light illumination measurement sensor), the measurement result thereof is used as a basis to control the light transmittance of the dimmer unit, or to control the luminance of images to be formed by the image forming unit.

As described above, with such control execution, i.e., control over the light transmittance of the dimmer unit based on the measurement result of the illumination sensor (environmental illumination measurement sensor), control over the luminance of images to be formed by the image forming unit based on the measurement result of the illumination sensor (environmental illumination measurement sensor), control over the light transmittance of the dimmer unit based on the measurement result of the second illumination sensor (transmitted-light illumination measurement sensor), and control over the luminance of images to be formed by the image forming unit based on the measurement result of the second illumination sensor (transmitted-light illumination measurement sensor), images to be viewed by a viewer are prevented from being degraded due to light from outside, and high-contrast images are obtained to be viewed by the viewer. Such control execution also optimizes the surrounding conditions for viewer's image viewing considering the illumination in the ambient environment where the display apparatus is disposed. The illumination sensors (environmental illumination measurement sensor and transmitted-light illumination measurement sensor) may be each a well-known illumination sensor, and may be each controlled by a well-known control circuit.

In the display apparatus including the second illumination sensor (transmitted-light illumination measurement sensor), desirably, the second illumination sensor (transmitted-light illumination measurement sensor) is provided closer to the viewer's side than to the light guide unit.

The dimmer unit may have the maximum light transmittance of 50%, and the minimum light transmittance of 30% or lower. The lowest possible light transmittance for the dimmer unit is 1%, for example.

When the illumination sensor (environmental illumination measurement sensor) shows the measurement result of a predetermined value (for convenience, sometimes referred to as “first illumination measurement value”) or higher, the dimmer unit may be adjusted to have the light transmittance of a predetermined value (for convenience, sometimes referred to as “first light transmittance”) or lower. When the illumination sensor (environmental illumination measurement sensor) shows the measurement result of a predetermined value (for convenience, sometimes referred to as “second illumination measurement value”) or lower, the dimmer unit may be adjusted to have the light transmittance of a predetermined value (for convenience, sometimes referred to as “second light transmittance”) or higher. Considering the illumination measured by the environmental illumination measurement sensor, when the transmitted-light illumination measurement sensor does not show the measurement result of a desired value, or when a delicate illumination adjustment is still expected, the dimmer unit may be adjusted in light transmittance at the same time with value monitoring of this second illumination sensor (transmitted-light illumination measurement sensor).

Herein, the first illumination measurement value is 10 lux, the first light transmittance takes any value in a range from 1% to 30%, the second illumination measurement value is 0.01 lux, and the second light transmittance takes any value in a range from 51% to 99%, for example. When the environmental illumination measurement sensor shows the measurement value of 1×10⁻³ lux or smaller, the dimmer unit is desirably increased in light transmittance as prompt as possible by reducing the drive time thereof through control over the drive voltage thereof, for example.

In some cases, light passing through the dimmer unit may be colored thereby as desired. The color selected by the dimmer unit may be variable or fixed. In the former, the dimmer unit may be a laminate structure including a dimmer for red, a dimmer for green, and a dimmer for blue, for example. In the latter, a color to be selected by the dimmer unit is not restrictive but may be brown, for example.

In the display apparatus according to the embodiment of the present disclosure, the dimmer unit may be smaller in size than the image display device, may be in the same size as the image display device, or may be larger in size than the image display device. Alternatively, in the projection image of the dimmer unit, the second deflection section may be positioned, or in the projection image of the second deflection section, the dimmer unit may be positioned.

In some cases, the dimmer unit may be provided to be detachable. In order to provide the dimmer unit to be detachable, the dimmer unit may be attached to the frame by using a screw made of transparent plastic, by forming a groove to the frame for engagement of the dimmer unit, or by providing a magnet to the frame. The frame may be also provided with a slide section to slide the dimmer unit thereinto. The dimmer unit may be provided with a connector for electrical connection to a control circuit via this connector and a wiring line. This control circuit is for controlling the light transmittance of the dimmer unit, and is provided in the control unit for controlling the image forming unit, for example. The dimmer unit may be bent.

The display apparatus according to the embodiment of the present disclosure may further include a microphone, and control the operation of the dimmer unit by an audio input using the microphone. Specifically, the dimmer unit may be controlled to operate/not to operate (turned ON/OFF) in response to a command issued by a viewer's voice. Alternatively, the display apparatus may further include an infrared light incident/exit unit to control the operation of the dimmer unit. Specifically, the infrared light incident/exit unit detects the viewer's blinking to control the dimmer unit to operate/not to operate.

In the display apparatus according to the embodiment of the present disclosure, a light shielding member may be provided to an area of the light guide unit where light coming from the image forming unit is input. This light shielding member is for shielding the light guide unit from the outside light, and such a display apparatus is referred to as “display apparatus according to a second embodiment of the present disclosure” for convenience. In the display apparatus according to the second embodiment of the present disclosure, with the light shielding member provided to an outside-light-entering area of the light guide unit for shielding the light guide unit from the outside light, even if the operation of the dimmer unit changes the amount of incoming outside light, this does not cause image degradation on the display apparatus with no undesired stray light because no outside light enters the outside-light-entering area of the light guide unit in the first place. Herein, the outside-light-entering area of the light guide unit is desirably included in the projection image of the light-shielding member toward the light guide unit.

The light shielding member may be provided to the light guide unit on the side not provided with the image forming unit, and is provided with a distance from the light guide unit. In the display apparatus in such a configuration, the light shielding member may be made of a non-transparent plastic material. This light shielding member may be integrally extended from the chassis of the image display device, may be attached to the chassis of the image display device, may be integrally extended from the frame, or may be attached to the frame. The light shielding member may be provided to an area of the light guide unit on the side not provided with the image forming unit, or may be provided to the dimmer unit. Herein, the light shielding member made of a non-transparent material may be formed on the surface of the light guide unit (e.g., specifically on the outer or inner surface of the protection member) by physical vapor deposition (PVD) or chemical vapor deposition (CVD), by printing, or by attaching thereto a film, a sheet, or a foil made of a non-transparent material, e.g., plastic material, metal material, or alloy material. The projection image of the end portion of the dimmer unit toward the light guide unit is desirably included in the projection image of the light-shielding member toward the light guide unit.

The display apparatus according to the embodiment of the present disclosure may configure a head mounted display (HMD), for example. This accordingly reduces the weight and size of the display apparatus, and the user's discomfort is significantly reduced when the user wears the display apparatus. Moreover, the manufacturing cost is also reduced.

The display apparatus according to the embodiment of the present disclosure may receive information and data from outside for image display in the image display device. With the display apparatus in such a configuration, the information and data relevant to images to be displayed on the image display device may be recorded, retained, and stored in a so-called cloud computer and a server. When the display apparatus is provided with a communication unit, e.g., a mobile phone or a smartphone, or when the display apparatus is used with a communication unit, this allows transmission/reception, and exchange of various types of information and data between the display apparatus and the cloud computer or the server. This also allows reception of various types of information and data for image display in the image display device. Alternatively, the various types of information and data for image display on the image display device may be recorded in the image display device.

The display apparatuses according to the first and second embodiments of the present disclosure including the above-mentioned various modifications may be available for displaying received electronic mails; for displaying various types of information in various sites on the Internet; for displaying various types of instructions about how to drive, operate, maintain, or disassemble a variety of devices, and symbols, codes, marks, emblems, patterns, and others therewith; for displaying various types of descriptions about people, products, and others, and symbols, codes, marks, emblems, patterns, and others therewith; for displaying moving and still images; for displaying subtitles in movies; for displaying descriptions about video or closed captions in synchronization with video display; for displaying explanations about acting performances, Kabuki, Noh, Kyogen, Operas, music recitals, ballet, theater plays, and others, and the details of story, the progress of story, and the background of story, and others therewith; for displaying explanations about amusement parks, art museums, tourist attractions, tourist spots, sightseeing signs, and others; and for displaying closed captions. For acting performances, Kabuki, Noh, Kyogen, Operas, music recitals, ballet, theater plays, amusement parks, art museums, tourist attractions, tourist spots, and sightseeing signs, the display apparatus may display relevant text as images whenever appropriate. Specifically, the display apparatus displays images based on the progress of story in movies or in acting performances, based on a predetermined schedule and time allocation, in response to an operator's operation, or in response to an incoming image control signal under the control of a computer or others, for example. For displaying various types of descriptions about devices, people, products, and others, viewing objects including devices, people, and products may be imaged using an imaging unit, and the imaging details may be analyzed in the display apparatus. In this manner, the display apparatus may be able to display various types of explanations created in advance about the viewing objects including devices, people, and objects. The image display apparatuses according to the first and second embodiments of the present disclosure may be each used as a stereoscopic display apparatus. In this case, the light guide unit may be detachably provided with a polarizer plate or film as appropriate, or the polarizer plate or film may be affixed to the light guide unit.

An image signal to the image forming unit includes not only text data but also luminance data about images to be displayed (luminance information), chromaticity data (chromaticity information), or both the luminance data and the chromaticity data, for example. The luminance data may correspond to the luminance at a predetermined area including an object viewed through the light guide unit, and the chromaticity data may correspond to the chromaticity at a predetermined area including an object viewed through the light guide unit. With an image signal including such luminance data about images, the images to be displayed become controllable in terms of luminance (brightness), and with an image signal including such chromaticity data about images, the images to be displayed become controllable in terms of chromaticity (color). Moreover, with an image signal including such luminance and chromaticity data about images, the images to be displayed become controllable in terms of both luminance (brightness) and chromaticity (color). When the luminance data in use corresponds to the luminance at a predetermined area including an object viewed through the image display device, the luminance data may be adjusted in value to increase the luminance of an image to be displayed, i.e., to make the image brighter when it is displayed, if the luminance at the predetermined area is increased. When the chromaticity data in use corresponds to the chromaticity at a predetermined area including an object viewed through the image display device, the chromaticity data may be adjusted in value to obtain, roughly, a complementary color relationship between the chromaticity at the predetermined area and the chromaticity of an image to be displayed. The complementary colors mean a pair of colors that are opposite each other on the color circle, e.g., red and green, yellow and purple, and blue and orange. The complementary colors also mean a pair of colors that produce a color with reduced chroma when mixed in appropriate proportions, e.g., white for light, and black for objects. However, the complementary characteristics are not the same in terms of visual effects when the colors are placed next to each other, and when the colors are mixed together. The complementary colors are also referred to as antagonistic colors, contrast colors, or opposing colors. Herein, the expression of “opposing colors” directly identifies which colors are opposite each other, whereas the expression of “complementary colors” identifies colors in a rather wider scope. The pair of complementary colors produces synergistic effects of enhancing their respective colors, and this is called complementary color harmony.

Embodiment 1

Embodiment 1 is about a display apparatus, an image display device, and a light guide unit according to the embodiments of the present disclosure. FIG. 1 is a conceptual view of the image display device in Embodiment 1, FIG. 2 is a schematic top view of the display apparatus in Embodiment 1 and the like, specifically a head mounted display (HMD), FIG. 3A is a schematic side view thereof, and FIG. 3B is a diagram schematically showing propagation of light in the light guide plate in the image display device. In FIGS. 2, 22A, 23A, 25, 31, 32, 33, 34, 35, 36, and 37, a housing member and the like are not shown.

The display apparatus in Embodiment 1 or in Embodiments 2 to 15 that will be described later is more specifically a head mounted display (HMD). Hereinafter, Embodiments 1 to 15 are collectively referred to as “Embodiment 1 and the like”. The display apparatus includes

(1) a frame mounted on the head portion of the viewer 20, e.g., eyeglass-shaped frame 10, and

(2) an image display device 100, 200, 300, or 400 attached to the frame 10. In this embodiment, the display apparatus in Embodiment 1 and the like is specifically of a binocular type including two image display devices, but may be a monocular type including one image display device. An image forming unit 111 or 211 offers image display in a color, e.g., green. The image display device 100, 200, 300, or 400 in Embodiment 1 and the like includes

(A) the image forming unit 111 or 211,

(B) a light guide unit 120 or 320, and

(C) an optical system (collimator light emitting optical system) 112 or 254 configured to collimate light coming from the image forming unit 111 or 211. The luminous flux as a result of collimation by the optical system 112 or 254 is input to the light guide unit 120 or 320, is guided therein, and is emitted therefrom. In the light guide unit (light guide section) 120 or 320, specifically, the light coming from the image forming unit 111 or 211 is input thereinto, guided therein, and emitted therefrom.

The light guide unit 120 or 320 in Embodiment 1 and the like includes

(a) a light guide plate 121 or 321 configured to emit the light provided by the image forming unit after the light is propagated therein by total reflection (light guide plate guiding the light of an image formed by the image forming unit),

(b) a first deflection section 130 or 330 configured to deflect at least part of the light input to the light guide plate 121 or 321 to achieve total reflection of the light in the light guide plate 121 or 321, and

(c) a second deflection section 140 or 340 configured to deflect the light propagated by total reflection in the light guide plate 121 or 321 to emit the light from the light guide plate 121 or 321.

The light guide unit 120 or 320 in Embodiment 1 and the like includes the light guide plate 121 of 321, and a housing member 160 that houses the light guide plate 121 of 321. The housing member 160 includes

a first cover member 161,

a second cover member 162 attached to the first cover member 161, and

an attachment member 165 configured to attach the light guide plate 121 or 321 to the housing unit 164 surrounded by the first cover member 161 and the second cover member 162. In the following description, for convenience, the first cover member 161 is positioned on the viewer's side, and the second cover member 162 is positioned on the outer side in relation to the first cover member 161.

The first cover member 161 and the second cover member 162 are fixed to each other by a frame member (support unit) 163. The frame member (support unit) 163 is disposed at and bonded to the outer edge portions of the first cover member 161 and the second cover member 162 by using an adhesive. The light guide plate 121 is attached to the frame member 163 via the attachment member 165. Specifically, the attachment member 165 attaches the light guide plate 121 to the housing unit 164 while being in contact with the both ends of the light guide plate 121 in a longitudinal direction, but may attach the light guide plate 121 to the housing unit 164 while being in contact with the entire outer circumferential portion of the light guide plate 121. The entire shape of the frame member 163 is frame-like and a cross-sectional shape thereof is substantially “L” shaped. A portion corresponding to the horizontal bar of the “L” on the lower side is bonded to the first cover member 161, and the top surface of a portion corresponding to the vertical bar of the “L” is bonded to the second cover member 162.

In Embodiment 1 and the like, the attachment member 165 is made of the thermal insulation material. Assuming that the light guide plate 121 or 321, the first cover member 161, and the second cover member 162 have the thermal conductivity of 1, the attachment member 165 has the thermal conductivity of 0.43, for example. The attachment member 165 made of the thermal insulation material is made of a thermal insulation resin material with a thickness of 0.01 mm to 1 mm (e.g., specifically 0.3 mm). Further, in Embodiment 1 and the like, the first cover member 161 and the second cover member 162 are each made of a material through which light passes. Specifically, the first cover member 161 and the second cover member 162 are each made of a resin material with a thickness of 0.01 mm to 1 mm (e.g., specifically 0.3 mm), with a length of 70 mm, for example, or with the width (height) of 70 mm, for example. The frame member 163 is made of a magnesium alloy with a thickness of 0.03 mm to 5 mm (e.g., specifically 4 mm). Further, the light guide plate 121 and the light guide plate 321 are each made of a resin material with a thickness of 0.01 mm to 3 mm (e.g., specifically 2 mm).

Alternatively, in Embodiment 1 and the like, the attachment member 165 is made of a buffer material.

Assuming that the light guide plate 121 or 321 has an elastic modulus of 1, the attachment member 165 has an elastic modulus of 5×10⁻⁴, for example. The material for the light guide plate 121 or 321 is as described above. Further, the attachment member 165 made of the buffer material is made of a low modulus adhesive with a thickness of 0.01 mm to 3 mm (e.g., specifically 2 mm).

Further, in Embodiment 1 and the like, a gap 164A is provided between the light guide plate 121 or 321 and the first cover member 161, and a gap 164B is provided between the light guide plate 121 or 321 and the second cover member 162. The gaps 164A and 164B each have the thickness of 0.01 mm to 2 mm (e.g., specifically 0.5 mm). Air is present in the gaps 164A and 164B. Alternatively, the gaps 164A and 164B may be filled with inert gas (e.g., nitrogen gas) or may be at reduced pressure.

In Embodiment 1 and the like, an ultraviolet ray protective layer (not shown) may be provided to an outer surface of the cover member (e.g., specifically to the second cover member 162) on the side to which outside light is input. Further, an antireflective layer (not shown) may be provided to the outer surface of the cover member (e.g., specifically to the first cover member 161) on the viewer's side, which is opposite to the side to which outside light is input. Alternatively, in order that the light from the collimator light emitting optical system 112 or 254 may be not reflected by the first cover member 161, a light shielding layer (not shown) may be formed in a part of the first cover member 161. The material for the ultraviolet ray protective layer, the antireflective layer, and the light shielding layer may be well-known material.

In Embodiment 1 and the like, the image display device 100, 200, 300, or 400 may be attached to the frame fixedly or detachably. The optical system 112 or 254 is disposed between the image forming unit 111 or 211 and the light guide unit 120 or 320. In such a configuration, the luminous flux as a result of collimation by the optical system 112 or 254 is input to the light guide unit 120 or 320, is guided therein, and is emitted therefrom. The light guide unit 120 or 320 is semi-transmissive (see-through type). Specifically, at least a part of the light guide unit facing the eyes of the viewer 20 (more specifically the light guide plate 121 or 321, and the second deflection section 140 or 340 that will be described later) may be semi-transmissive (see-through), and through such a part of the light guide unit, the viewer may see the outside view.

In Embodiment 1 and the like, in a light beam emitted from the center of the image forming unit 111 or 211 and passed through a node in the optical system 112 or 254 on the side of the image forming unit (center light beam CL), a part of the center light beam vertically enters the light guide unit 120 or 320 (at-center incident light beam). The point at which the at-center incident light beam enters the light guide unit 120 or 320 is referred to as “light-guide-unit center point O”. The axis passing through the light-guide-unit center point O, and being parallel to the axis of the light guide unit 120 or 320 is referred to as “X axis”, and the axis passing through the light-guide-unit center point O, and coinciding with the normal to the light guide unit 120 or 320 is referred to as “Z axis”. The center point of the first deflection section 130 or 330 that will be described next is the light-guide-unit center point O. That is, as shown in FIG. 3B, in the image display device 100, 200, 300, or 400, the center light beam CL emitted from the center of the image forming unit 111 or 211 and passed through a node in the optical system 112 or 254 on the side of the image forming unit bumps on the light guide plate 121 or 321 in the vertical direction. In other words, the center light beam CL enters the light guide plate 121 or 321 at an angle of 0 degrees. In this case, the center of an image to be displayed coincides with the normal to the first plane 122 or 322 of the light guide plate 121 or 321.

In Embodiment 1 or Embodiment 2 that will be described later, the first and second deflection sections 130 and 140 are both disposed in the light guide plate 121. The first deflection section 130 reflects light input to the light guide plate 121, and the second deflection section 140 passes therethrough and reflects the light for a plurality of times after the light is propagated by total reflection in the light guide plate 121. That is, the first deflection section 130 serves as a reflection mirror, and the second deflection section 140 serves as a semi-transmissive mirror.

More specifically, the first deflection section 130 provided in the light guide plate 121 is made of aluminum (Al), and is configured by a light reflection film (a kind of mirror) that reflects the light input to the light guide plate 121. On the other hand, the second deflection section 140 also provided in the light guide plate 121 is configured by a multi-layer film structure of a plurality of dielectric layers. The dielectric multi-layer film includes a layer of TiO₂ (titanium dioxide) being a high dielectric material, and a layer of SiO₂ (silicon dioxide) being a low dielectric material. The multi-layer film structure of a plurality of dielectric layers is described in Japanese Unexamined Patent Application Publication No. 2005-521099. A dielectric six-layer film is exemplarily shown, but this is not restrictive. In the structure, a dielectric layer and another dielectric layer include therebetween a very thin layer made of the same material as the light guide plate 121. In the first deflection section 130, the collimated light input to the light guide plate 121 is reflected (or diffracted) so as to achieve total reflection of the collimated light in the light guide plate 121. On the other hand, in the second deflection section 140, the collimated light is reflected (or diffracted) for a plurality of times after the light is propagated by total reflection in the light guide plate 121, and remains collimated when it is emitted from the light guide plate 121 toward the eyes 21 of the viewer 20.

In order to provide the first deflection section 130 in the light guide plate 121, the light guide plate 121 is partially cut out to obtain a sloped surface, i.e., cut-out portion 124, and the resulting sloped surface is provided thereon with a light reflection film, i.e., first deflection section 130, by vapor deposition. The cut-out portion 124 is then attached to the first deflection section 130. Moreover, for use as the second deflection section 140, formed is a multi-layer film structure of a plurality of layers made of the same material as the light guide unit 121, e.g., glass, and a plurality of dielectric layers (e.g., formed by vapor deposition). The light guide plate 121 is then partially cut out to obtain a sloped surface, i.e., cut-out portion 125, and the resulting sloped surface is provided thereon with the multi-layer structure. The resulting structure is then put in shape by abrasion, for example. This obtains the light guide unit 120 including the light guide plate 121 formed therein with the first and second deflection sections 130 and 140.

In Embodiment 1 and the like, the light guide plate 121 or 321 includes two parallel planes (the first plane 122 or 322, and the second plane 123 or 323) extending parallel to the direction of light propagation (X axis) by total reflection in the light guide plate 121 or 321. The first plane 122 or 322 and the second plane 123 or 323 are opposed to each other. Collimated light enters the first plane 122 or 322 being the light incident plane, and then exits from the first plane 122 or 322 being the light exit plane after the light is propagated by total reflection in the light guide plate. However, this is not restrictive, and the second plane 123 or 323 may serve as the light incident plane, and the first plane 122 or 322 may serve as the light exit plane. The first plane 122 or 322 of the light guide plate 121 or 321 is opposed to the first cover member 161, and the second plane 123 or 323 of the light guide plate 121 or 321 is opposed to the second cover member 162.

In Embodiment 1 or Embodiment 3 that will be described later, the image forming unit 111 is the image forming unit having a first configuration, and includes a plurality of pixels arranged in a 2D matrix. Specifically, the image forming unit 111 includes a reflective spatial light modulator 150, and a light source 153 configured by a light-emitting diode that emits white light. The image forming unit 111 is housed as a whole in a chassis 113 (indicated by alternate long and short dashed lines in FIG. 1). The chassis 113 is provided with an aperture (not shown), and through this aperture, light is emitted from the optical system 112, i.e., collimator light emitting optical system or collimator optical system. The first cover member 161 is attached to the chassis 113. The reflective spatial light modulator 150 is configured by a liquid crystal display (LCD) 151 configured by an LCOS as a light valve, and a polarized beam splitter 152. With the polarized beam splitter 152, light coming from the light source 153 is partially reflected and then is directed to the liquid crystal display 151, and the light reflected by the liquid crystal display 151 is partially passed therethrough and is directed to the optical system 112. The liquid crystal display 151 includes a plurality of, e.g., 640×480 pieces of, pixels (liquid crystal cells) arranged in a 2D matrix. The polarized beam splitter 152 is in the well-known structure and configuration. The not-polarized light coming from the light source 153 bumps on the polarized beam splitter 152. The polarized beam splitter 152 passes therethrough any P-polarized components, and emits the components to the outside of the system. On the other hand, the polarized beam splitter 152 reflects any S-polarized components. The S-polarized components are then input to the liquid crystal display 151, are reflected therein, and are emitted therefrom. In the light emitted from the liquid crystal display 151, light beams emitted from “white” pixels contain a high proportion of P-polarized components, and light beams emitted from “black” pixels contain a high proportion of S-polarized components.

Therefore, in the light emitted from the liquid crystal display 151 and bumped on the polarized beam splitter 152, the P-polarized components pass through the polarized beam splitter 152, and are then guided to the optical system 112.

On the other hand, the S-polarized components are reflected by the polarized beam splitter 152, and are then put back to the light source 153. The optical system 112 is a convex lens, for example, and at the focal length in the optical system 112, the image forming unit 111 (more specifically, the image display device 151) is disposed for generating collimated light.

In Embodiment 1 and the like, the frame 10 is configured by a front section 11, two temple sections 13, and two temple tip sections 14. The front section 11 is disposed to be in front of the viewer 20, and the two temple sections 13 are respectively attached to the ends of the front section 11 via hinges 12 to be able to rotate. The temple tip sections 14 are also referred to as tip cells or ear pads, and are respectively attached to tip end portions of the temple sections 13. The frame 10 is provided also with a nose pad (not shown in FIG. 2). That is, the structure including the frame 10 and the nose pad looks substantially the same as that of ordinary glasses. What is more, the temple sections 13 are each provided with the chassis 113 to be detachable by a retention member 19. Alternatively, the frame member 163 may be attached to the front section 11 while the first cover member 161 is bonded to the chassis 113. The frame 10 is made of metal or plastic. The temple sections 13 may be each provided with the chassis 113 not to be detachable by the retention member 19. For a user owning and wearing glasses, in the user's glasses, temple sections of the frame may be each provided with the chassis 113 to be detachable by the retention member 19. The chassis 113 may be attached inside or outside of each of the temple sections 13.

A wiring line (signal line or power supply line) 15 from one image forming unit 111A goes through the temple section 13 and the temple tip section 14 to be outside from the tip end portion of the temple tip section 14, and then is connected to a control unit (control circuit or control section) 18. The image forming unit 111A and another image forming unit 111B are each provided with a headphone section 16, and a headphone-use wiring line 16′ from each of the image forming units 111A and 111B goes through the temple section 13 and the temple tip section 14 to reach the headphone section 16 via the tip end portion of the temple tip section 14. More specifically, the headphone-use wiring line 16′ goes around behind the pinna from the tip end portion of the temple tip section 14, and reaches the headphone section 16. Such a configuration simplifies the display apparatus without giving a viewer an impression that the headphone sections 16 and the headphone-use wiring lines 16′ do not look tidy.

As described above, the wiring line (signal line or power supply line) 15 is connected to the control unit (control circuit) 18. The control unit 18 is provided with an image information storage unit 18A, for example. The control unit 18 performs processing for image display. The control unit 18 and the image information storage unit 18A may be each configured by a well-known circuit.

At a center portion 11′ of the front section 11, an imaging unit 17 may be attached using any appropriate attachment member (not shown). The imaging unit 17 is one configured by a solid-state imaging element being a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor, and a lens (these are not shown). Signals from the imaging unit 17 are sent to the image forming unit 111A via a wiring line (not shown) extending from the imaging unit 17, for example.

As an example, the control unit (control circuit, control section) 18 provided in the display apparatus is incorporated with a communication unit (receiver), or the display apparatus includes a communication section (receiver) such as mobile phone or smartphone. In the display apparatus, information and data relevant to images to be displayed on the image display device may be recorded, retained, and stored in a so-called cloud computer and a server. This allows transmission/reception, and exchange of various types of information and data between the display apparatus and the cloud computer or the server. This also allows reception of signals based on various types of information and data, i.e., signals for image display on the image display device, and allows the receiver to receive the signals. When the display apparatus receives the signals for image display on the image display device 100, 200, 300, or 400, e.g., electronic mails and various types of information in a variety of sites on the Internet, the image display device 100, 200, 300, or 400 accordingly displays such electronic mails and various types of information. At this time, as will be described later, a dimmer unit 700 may be changed in light transmittance under the control of the control unit 18. Alternatively, the signals for image display on the image display device 100, 200, 300, or 400 may be stored in the image display device, e.g., specifically in the image information storage unit 18A in the control unit 18.

In the light guide unit, the image display device, and the display apparatus in Embodiment 1 described above, the housing member includes the first cover member, the second cover member, and the attachment member, and the light guide plate is attached in the housing member via the attachment member. This hardly causes problems such as warpage of a light guide plate, which results from a difference in temperature of surrounding environments and the like.

Embodiment 2

Embodiment 2 is a modification of Embodiment 1. As shown in FIG. 4, i.e., the conceptual view of the image display device 200 in a display apparatus (head mounted display) in Embodiment 2, in Embodiment 2, an image forming unit 211 is the image forming unit having a second configuration. That is, the image forming unit 211 includes a light source 251, and a scanning section 253 that scans collimated light coming from the light source 251. To be more specific, the image forming unit 211 includes

(1) the light source 251,

(2) a collimator optical system 252 configured to collimate light coming from the light source 251,

(3) the scanning section 253 configured to scan collimated light coming from the collimator optical system 252, and

(4) a relay optical system 254 configured to relay and emit the collimated light after the light is scanned by the scanning section 253. Herein, the image forming unit 211 is housed as a whole in a chassis 213 (indicated by alternate long and short dashed lines in FIG. 4). The chassis 213 is provided with an aperture (not shown), and through this aperture, light is emitted from the relay optical system 254. The chassis 213 is detachably attached to the temple section 13 by the retention section 19. The first cover member 161 is attached to the chassis 213.

The light source 251 is a light-emitting element that emits white light. Light from the light source 251 enters the collimator optical system 252 having the positive optical power as a whole, and is collimated and emitted. This collimated light is then reflected by a total-reflection mirror 256, and then is horizontally and vertically scanned by the scanning section 253. This scanning section 253 is configured by a MEMS in which a micro mirror is rotatable in the 2D direction so that the collimated light is scanned two-dimensionally. A kind of 2D image is then formed, and virtual pixels are generated (e.g., the number of the pixels is the same as those in Embodiment 1). Light from these virtual pixels passes through the relay optical system (collimator light emitting optical system) 254 configured by a well-known relay optical system, and luminous flux being the collimated light enters the light guide unit 120.

The light guide unit 120 that receives, guides, and emits the luminous flux being the collimated light obtained in the relay optical system 254 is in the same structure and configuration as the light guide unit described in Embodiment 1, and thus is not described in detail again. Moreover, as described above, the display apparatus in Embodiment 2 is substantially in the same structure and configuration as the display apparatus in Embodiment 1 except for the image forming unit 211, and thus is not described in detail again.

Embodiment 3

Embodiment 3 is also a modification of Embodiment 1. FIG. 5 is a conceptual view of the image display device 300 in a display apparatus (head mounted display) in Embodiment 3. FIG. 6 is a schematic cross-sectional view of a partially-enlarged reflective volumetric holographic diffraction grating. In Embodiment 3, the image forming unit 111 is the image forming unit having a first configuration similarly in Embodiment 1. The light guide unit 320 is basically the same as the light guide unit 120 in Embodiment 1 in terms of structure and configuration except for first and second deflection sections.

In Embodiment 3, the first and second deflection sections are provided on the surface of the light guide plate 321 (specifically on the second plane 323 of the light guide plate 321). The first deflection section diffracts and reflects light input to the light guide plate 321, and the second deflection section diffracts and reflects the light for a plurality of times after the light is propagated by total reflection in the light guide plate 321. Herein, the first and second deflection sections are each a diffraction grating element, specifically a reflective diffraction grating element, and more specifically a reflective volumetric holographic grating element. In the description below, for convenience, the first deflection section being a reflective volumetric holographic diffraction grating is referred to as “first diffraction grating member 330”, and the second deflection section being a reflective volumetric holographic diffraction grating is referred to as “second diffraction grating member 340”.

In Embodiment 3 or Embodiment 4 that will be described later, the first and second diffraction grating members 330 and 340 are each a laminate structure of a single diffraction grating layer. The diffraction grating layers are each made of photopolymer, and are each manufactured in the previous manner with an interference pattern formed to correspond to one wavelength band (or wavelength). The interference pattern formed on the diffraction grating layer (diffraction optical element) is constant in pitch, and is linear and parallel to the Y axis. The axes of the first and second diffraction grating members 330 and 340 are both parallel to the X axis, and the normal thereto are parallel to the Z axis.

FIG. 6 is a schematic cross-sectional view of a partially-enlarged reflective volumetric holographic diffraction grating. The reflective volumetric holographic diffraction grating is provided with an interference pattern with a desired slant angle of φ. Herein, the slant angle φ means an angle formed between the surface of the reflective volumetric holographic diffraction grating and the interference pattern. The interference pattern is formed from the inside to the surface of the reflective volumetric holographic diffraction grating. The interference pattern satisfies Bragg's Law. Herein, Bragg's Law means a condition satisfying Equation A below. In Equation A, m denotes a positive integer, λ denotes a wavelength, d denotes a grating surface pitch (normal interval on virtual plane including interference pattern), and Θ denotes a complementary angle of light entering the interference pattern. Equation B shows the relationship between the complementary angle Θ, the slant angle φ, and an incident angle φ when light enters the diffraction grating member at the incident angle φ.

m*λ=2*d*sin(Θ)   A

Θ=90°−(φ+φ)   B

As described above, the first diffraction grating member 330 is disposed (attached) on the second plane 323 of the light guide plate 321, and as to collimated light input to the light guide plate 321 from the first plane 322, diffracts and reflects the light to achieve total reflection thereof in the light guide plate 321. Also as described above, the second diffraction grating member 340 is disposed (attached) on the second plane 323 of the light guide plate 321, and diffracts and reflects the collimated light for a plurality of times after the light is propagated by total reflection in the light guide plate 321.

The light remains collimated when it is emitted from the first plane 322 of the light guide plate 321.

Also from the light guide plate 321, the collimated light is emitted after the light is propagated by total reflection therein. The light guide plate 321 is thin, and thus an optical path is long for the light to propagate therein. Therefore, the light is reflected a different number of times depending on the viewing angle before reaching the second diffraction grating member 340. More in detail, in the collimated light entering the light guide plate 321, a part of the light entering the light guide plate 321 at an angle in the direction of being closer to the second diffraction grating member 340 is reflected less often than a part of the light entering the light guide plate 321 at an angle in the direction of being away from the second diffraction grating member 340. This is because, in the collimated light diffracted and reflected on the first diffraction grating member 330, the collimated light entering the light guide plate 321 at an angle in the direction of being closer to the second diffraction grating member 340 forms an angle smaller than the collimated light entering the light guide plate 321 at an angle in the opposite direction. This angle is formed with the normal to the light guide plate 321 when the light propagating in the light guide plate 321 bumps on the inner surface thereof. The interference patterns formed in the first and second diffraction gating members 330 and 340 are symmetrical with respect to the virtual plane, which is vertical to the axis of the light guide plate 321.

The light guide plate 321 in Embodiment 4 that will be described later is basically the same as the light guide plate 321 described above in terms of structure and configuration.

As described above, the display apparatus in Embodiment 3 is substantially in the same structure and configuration as the display apparatus in Embodiment 1 except for the light guide unit 320, and thus is not described in detail again.

Embodiment 4

Embodiment 4 is a modification of Embodiment 3. FIG. 7 is a conceptual view of an image display device in a display apparatus (head mounted display) in Embodiment 4. The components in the image display device 400 in Embodiment 4, i.e., the light source 251, the collimator optical system 252, the scanning section 253, the collimator light emitting optical system (relay optical system 254), and others, are in the same structure and configuration as those in Embodiment 2 (image forming unit having a second configuration). The light guide unit 320 in Embodiment 4 is in the same structure and configuration as the light guide unit 320 in Embodiment 3. The display apparatus in Embodiment 4 is substantially in the same structure and configuration as the display apparatus in Embodiment 2 except for the above differences, and thus is not described in detail again.

Embodiment 5

Embodiment 5 is a modification of the housing member described in Embodiments 1 to 4. In the following description, the image display device described in Embodiment 1 is described as an example, but it is applicable to the image display devices described in Embodiments 2 to 4 as a matter of course.

As shown in conceptual views of FIGS. 8 and 9, the light guide plate 121 is attached to the frame member (support unit) 163 by the attachment member 165. The shape of the frame member 163 is frame-like, and the light guide plate 121 is attached to the opposing inner side surfaces of the frame-like portion by the attachment member 165.

Alternatively, as shown in a conceptual view of FIG. 10, the first cover member 161 and the second cover member 162 are bonded to each other via a protrusion (support unit) 163A formed at the outer edge portion of the first cover member 161. The light guide plate 121 is attached to the second cover member 162 by the attachment member 165. Alternatively, as shown in a conceptual view of FIG. 11, the first cover member 161 and the second cover member 162 are bonded to each other via a protrusion (support unit) 163B formed at the outer edge portion of the second cover member 162. Thus, the light guide plate 121 is attached to the first cover member 161 by the attachment member 165.

Alternatively, as shown in conceptual views of FIGS. 12 and 13, the first cover member 161 and the second cover member 162 are fixed to each other by the frame member (support unit) 163, and the light guide plate 121 is attached to the first cover member 161 via the attachment member 165 or attached to the second cover member 162 via the attachment member 165.

In the various forms described above, the attachment member 165 may attach the light guide plate 121 to the housing unit 164 while being in contact with the entire outer circumferential portion of the light guide plate 121, or while being in contact with the outer circumferential portion of the light guide plate 121 at two spots (two areas, e.g., two ends of the light guide plate 121 in the longitudinal direction).

Alternatively, as shown in a conceptual view of FIG. 14, the light guide plate 121 may be attached to the frame member 163 at one or a plurality of spots by an attachment member 166 formed of a screw or a spring (e.g., leaf spring).

In Embodiments 3 and 4, the light guide unit is configured by a piece of light guide plate. For color image display, however, first, second, and third light guide plates 321R, 321G, and 321B may be stacked together with intervals thereamong as shown in a conceptual view of FIG. 15. That is, the first light guide plate 321R is provided with a diffraction grating member (not shown) being a layer of reflective volumetric holographic diffraction grating that diffracts and reflects light in a red wavelength band (or with a red wavelength). The second light guide plate 321G is provided with a diffraction grating member (not shown) being a layer of reflective volumetric holographic diffraction grating that diffracts and reflects light in a green wavelength band (or with a green wavelength). The third light guide plate 321B is provided with a diffraction grating member (not shown) being a layer of reflective volumetric holographic diffraction grating that diffracts and reflects light in a blue wavelength band (or with a blue wavelength).

The first cover member 161 and the second cover member 162 are each made of PMMA with the thickness of 1.0 mm, the light guide plate is made of resin with the thickness of 1.0 mm, and the frame member 163 is made of magnesium alloy with the thickness of 3.5 mm. By using an adhesive 167 with the thickness of 0.1 mm, the first and second light guide plates 321R and 321G are bonded together at their end portions, and the second and third light guide plates 321G and 321B are bonded together at their end portions. The interval between the first and second light guide plates 321R and 321G is 0.5 mm, and the interval between the second and third light guide plates 321G and 321B is 0.1 mm.

Further, a gap (air layer) 164 is 0.1 mm. Moreover, the second light guide plate 321G is attached to the housing unit 164 by the attachment member 165 made of resin material with the thickness of 0.1 mm and being in contact with the entire outer circumferential portion of the second light guide plate 321G. Specifically, the shape of the frame member 163 is frame-like, and the second light guide plate 321G is attached to the opposing inner side surfaces of the frame-like portion by the attachment member 165.

In such a light guide unit, a simulation was performed to determine how large temperature difference was caused between the first plane and the second plane of the light guide plate, when a temperature difference of 1° C. was caused between the first cover member 161 and the second cover member 162. As a result, in the three light guide plates 321R, 321G, and 321B, the largest temperature difference in the light guide plates was 0.06° C. On the other hand, as a comparable example, a similar simulation was performed using a light guide unit from which the first cover member 161 and the second cover member 162 are removed. As a result, the largest temperature difference in the light guide plates was 0.23° C. Assuming that the amount of warpage of the light guide plate having the largest temperature difference in the comparable example was “1.0”, the amount of warpage of the light guide plate having the largest temperature difference in Embodiments was 0.46.

Alternatively, at least one of the cover members is provided with an opening. Specifically, as shown in a conceptual view of FIG. 16, the first cover member 161 may be provided with an opening 168. This allows the light from the collimator light emitting optical system 112 to be prevented from being reflected on the first cover member 161. It is desirable that the opening 168 provided to the first cover member 161 be shaped such that the light from the collimator light emitting optical system 112 does not impinge on the first cover member 161. Alternatively, as shown in a conceptual view of FIG. 17, the second cover member 162 may be provided with an opening 168. The shape of the opening 168 provided to the second cover member 162 may be inherently arbitrarily set, e.g., may be rectangular.

Further, as shown in a conceptual view of FIG. 18, the first cover member 161 and the second cover member 162 may be each provided with the opening 168.

Alternatively, as shown in a conceptual view of FIG. 19, a resin layer 169 is provided between the light guide plate 121 and the first cover member 161, and a resin layer 169 is provided between the light guide plate 121 and the second cover member 162. In other words, the inside of the housing member 160 may be filled with the resin layer 169. In this case, it is desirable that the resin layer 169 have the thermal conductivity smaller than the thermal conductivity of the light guide plate 121, the first cover member 161, and the second cover member 162. Examples of the material for the resin layer 169 may include thermosetting resin and ultraviolet curable resin such as epoxy-based resin and acrylic-based resin.

Embodiment 6

Embodiment 6 is a modification of Embodiments 1 to 5, and as shown in a conceptual view of FIG. 20, the dimmer unit 700 is attached to the cover member on the side to which outside light is input (specifically, to the second cover member 162). The dimmer unit 700 is provided on the side of the light guide unit 120 or 320 not provided with the image forming unit 111 or 211 so as to adjust the amount of light that is input from the outside. Specifically, using an adhesive 707, the dimmer unit 700 being a kind of optical shutter is fixed to the light guide unit 120 or 320 (specifically, to the second cover member 162). The dimmer unit 700 is provided to the area of the light guide unit 120 or 320 on the side opposite to the viewer 20.

The dimmer unit 700 in Embodiment 6 is an optical shutter in which a light-transmission control material layer 705 is made of a liquid crystal material. That is, the dimmer unit 700 includes

transparent first and second substrates 701 and 703, the first substrate 701 opposing the light guide unit 120, the second substrate 703 opposing the first substrate 701,

first and second electrodes 702 and 704 respectively provided to the first and second substrates 701 and 703, and

the light-transmission control material layer 705 sealed between the first and second substrates 701 and 703.

Herein, the first and second substrates 701 and 703 are each made of a plastic material. The first and second electrodes 702 and 704 are each a transparent electrode made of ITO (indium tin oxide), and are each formed by a combination of PVD such as sputtering and lifting off. The light-transmission control material layer 705 is specifically a liquid crystal layer made of a TN (Twisted Nematic) liquid crystal material. The first and second electrodes 702 and 704 are not patterned, and are so-called solid electrodes. However, the first and second electrodes 702 and 704 may be patterned as appropriate. The first and second electrodes 702 and 704 are connected to the control unit 18 via connectors and wiring lines that are not shown.

The first and second substrates 701 and 703 are sealed together at outer edge portions using a sealing agent 706. The first substrate 701 of the dimmer unit 700 and the second cover member 162 are attached together by the adhesive 707. The first and second substrates 701 and 703 are each provided with a polarizer film on the outer surface, but these polarizer films are not shown. The first substrate 701 in the dimmer unit 700 is shorter than the light guide plate 121, and the first substrate 701 in the dimmer unit 700 is fixed to the second cover member 162 using the adhesive 707. The adhesive 707 is provided at the outer edge portion of the first substrate 701. This is applicable also to other Embodiments to be described below.

The light guide unit 120 and the dimmer unit 700 are disposed in this order from the viewer's side.

The dimmer unit 700 is controlled in light transmittance by voltage to be applied to the first and second electrodes 702 and 704. Specifically, when voltage is applied to the first electrode 702 while the second electrode 704 is grounded, for example, this causes a change of liquid crystal alignment in the liquid crystal layer configuring the light-transmission control material layer 705 so that the light transmittance is changed in the liquid crystal layer (refer to FIGS. 21A and 21B). For voltage application to the first and second electrodes 702 and 704, a viewer may operate a control knob provided to the control unit 18. That is, the viewer may adjust the light transmittance of the dimmer unit 700 while viewing images provided by the light guide unit 120 or 320.

As described above, with the display apparatus in Embodiment 6, the image display device offers satisfactory images to the viewer with no disturbance by the outside light.

In Embodiment 6 described above, the dimmer unit 700 is attached to the image display device 100, i.e., the dimmer unit 700 is specifically attached to the light guide unit 120. Alternatively, the dimmer unit 700 may be attached to the frame 10, or to the chassis 113.

The dimmer unit 700 may be ON at all times, may be operated/not operated (turned ON/OFF) in response to a viewer's command (operation), or may be OFF under normal conditions and may start operating in response to a signal for image display on the image display device 100, 200, 300 or 400. In order to be operated/not operated in response to a viewer's command (operation), the display apparatus may be further provided with a microphone, and may control the operation of the dimmer unit 700 in response to an audio input via the microphone, for example. Specifically, the dimmer unit may be controlled to operate/not to operate in response to a command issued by a viewer's voice. Alternatively, the display apparatus may further include an infrared light incident/exit unit, and using this infrared light incident/exit unit, may control the operation of the dimmer unit 700. That is, a viewer's blinking may be detected using the infrared light incident/exit unit to control the dimmer unit 700 to operate/not to operate.

Embodiment 7

Embodiment 7 is a modification of Embodiment 6. FIG. 22A is a schematic top view of a display apparatus in Embodiment 7, and FIG. 22B is a schematic view of a circuit that controls an illumination sensor. The display apparatus in Embodiment 7 is further provided with a sensor 801 that measures the brightness in the outside environment. Based on the measurement result of outside brightness obtained by the sensor (hereinafter referred to as “first illumination sensor” for convenience) 801, a part of the dimmer unit 700 is changed in light transmittance.

That is, the display apparatus in Embodiment 7 is further provided with the first illumination sensor (environmental illumination measurement sensor) 801 that measure the illumination in the environment where the display apparatus is disposed. The display apparatus controls the light transmittance of the dimmer unit 700 based on the measurement result of the first illumination sensor 801. Together with or separately from the control over the light transmittance, the display apparatus controls the luminance of images to be formed by the image forming unit 111 or 211 based on the measurement result of the first illumination sensor 801. The first illumination sensor 801 in the well-known structure and configuration may be provided to the outer end portion of the light guide unit 120 or 320, or to the outer end portion of the dimmer unit. The first illumination sensor 801 is connected to the control unit 18 via connectors and wiring lines that are not shown. The control unit 18 includes a circuit for controlling the first illumination sensor 801. This circuit for controlling the first illumination sensor 801 is configured by an illumination calculation circuit, a comparison calculation circuit, and an environmental illumination measurement sensor control circuit. The illumination calculation circuit calculates the illumination based on the measurement value provided by the first illumination sensor 801. The comparison calculation circuit compares the calculation result of the illumination calculation circuit, i.e., illumination value, with a standard value. The environmental illumination measurement sensor control circuit controls the dimmer unit 700 and/or the image forming unit 111 or 211 based on the value obtained by the comparison calculation circuit. These circuits may be each a well-known circuit. For controlling the dimmer unit 700, the light transmittance therein is controlled, and for controlling the image forming unit 111 or 211, the luminance of images to be formed thereby is controlled. Herein, the control over the light transmittance in the dimmer unit 700 and the control over the luminance of images formed by the image forming unit 111 or 211 may be executed separately or executed in correlation with each other.

As an example, when the first illumination sensor 801 shows the measurement result of a predetermined value (first illumination measurement value) or higher, the dimmer unit 700 is adjusted to have the light transmittance of a predetermined value (first light transmittance) or lower. On the other hand, when the first illumination sensor 801 shows the measurement result of a predetermined value (second illumination measurement value) or lower, the dimmer unit 700 is adjusted to have the light transmittance of a predetermined value (second light transmittance) or higher. The first illumination measurement value may be 10 lux, the first light transmittance may take any value in a range from 1% to 30% inclusive, the second illumination measurement value may be 0.01 lux, and the second light transmittance may take any value in a range from 51% to 99% inclusive, for example.

The first illumination sensor (environmental illumination measurement sensor) 801 in Embodiment 7 is applicable to the display apparatuses described in Embodiments 2 to 5. When the display apparatus is provided with an imaging unit, the first illumination sensor 801 may be configured by light-receiving elements provided to the imaging unit for exposure measurement.

In the display apparatus in Embodiment 7 or Embodiment 8 that will be described next, the light transmittance of the dimmer unit is controlled based on the measurement result of the first illumination sensor (environmental illumination measurement sensor), and the luminance of images to be formed by the image forming unit is controlled also based on the measurement result of the first illumination sensor. Moreover, as will be described next, the light transmittance of the dimmer unit is controlled based on the measurement result of the second illumination sensor (transmitted-light illumination measurement sensor), and the luminance of images to be formed by the image forming unit is controlled also based on the measurement result of the second illumination sensor. Such control execution offers high-contrast images to be viewed by a viewer, and also optimizes the surrounding conditions for viewer's image viewing considering the illumination in the ambient environment where the display apparatus is disposed.

Embodiment 8

Embodiment 8 is also a modification of Embodiment 6. FIG. 23A is a schematic top view of a display apparatus in Embodiment 8, and FIG. 23B is a schematic view of a circuit that controls an illumination sensor.

The display apparatus in Embodiment 8 measures the illumination based on light passed through the dimmer unit from the outside environment. That is, the display apparatus is further provided with a second illumination sensor (transmitted-light illumination measurement sensor) 802 that measures the illumination of environment light, i.e., whether the light is adjusted to have a desired value of illumination after passing through the dimmer unit. The measurement result of the second illumination sensor 802 is used as a basis to control the light transmittance of the dimmer unit 700. Together with or separately from the control over the light transmittance, the display apparatus controls the luminance of images to be formed by the image forming unit 111 or 211 based on the measurement result of the second illumination sensor 802. The second illumination sensor 802 in the well-known structure and configuration is provided closer to the viewer's side than the light guide unit 120 or 320. Specifically, the second illumination sensor 802 may be provided to the surface of the light guide unit 121 or 321 on the viewer's side. The second illumination sensor 802 is connected to the control unit 18 via connectors and wiring lines that are not shown. The control unit 18 includes a circuit for controlling the second illumination sensor 802. This circuit for controlling the second illumination sensor 802 is configured by an illumination calculation circuit, a comparison calculation circuit, and a transmitted-light illumination measurement sensor control circuit. The illumination calculation circuit calculates the illumination based on the measurement value provided by the second illumination sensor 802. The comparison calculation circuit compares the calculation result of the illumination calculation circuit, i.e., illumination value, with a standard value. The transmitted-light illumination measurement sensor control circuit controls the dimmer unit 700 and/or the image forming unit 111 or 211 based on the value obtained by the comparison calculation circuit. These circuits may be each a well-known circuit. For controlling the dimmer unit 700, the light transmittance therein is controlled, and for controlling the image forming unit 111 or 211, the luminance of images to be formed thereby is controlled. Herein, the control over the light transmittance in the dimmer unit 700 and the control over the luminance of images formed by the image forming unit 111 or 211 may be executed separately or executed in correlation with each other. Considering the illumination measured by the first illumination sensor 801, when the measurement result of the second illumination sensor 802 shows that the illumination is not controlled to obtain a desired value of illumination, i.e., the measurement result of the second illumination sensor 802 is not of a desired value of illumination, or when a delicate illumination adjustment is still expected, the dimmer unit may be adjusted in light transmittance at the same time with value monitoring of the second illumination sensor 802.

The second illumination sensor (transmitted-light illumination measurement sensor) 802 in Embodiment 8 is applicable to the display apparatuses described in Embodiments 2 to 5. Alternatively, the second illumination sensor 802 in Embodiment 8 may be combined with the first illumination sensor 801 in Embodiment 7 for use. If this is the case, with various tests, the control over the light transmittance in the dimmer unit 700 may be executed separately from or in correlation with the control over the luminance of images to be formed by the image forming unit 111 or 211.

Embodiment 9

Embodiment 9 is a modification of Embodiments 1 to 8, and is about the display apparatus according to the second embodiment of the present disclosure. FIG. 24 is a conceptual view of an image display device in Embodiment 9, and FIG. 25 is a schematic top view of the display apparatus (specifically head mounted display (HMD)) in Embodiment 9.

In the display apparatus in Embodiment 9, a light shielding member 710 is provided to an area of the light guide unit 120 where light coming from the image forming unit 111A or 111B is input, specifically to an area where the first deflection section 130 is provided. This light shielding member 710 is for shielding the light guide unit 120 from the outside light. Herein, the projection image of the light shielding member 710 toward the light guide unit 120 includes the area of the light guide unit 120 where the light coming from the image forming unit 111A or 111B is input. The projection image of the light shielding member 710 toward the light guide unit 120 also includes the projection image of the end portion of the dimmer unit 700 toward the light guide unit 120.

In Embodiment 9, the light shielding member 710 is provided to the light guide unit 120 on the side not provided with the image forming unit 111A or 111B, and is provided with a distance from the light guide unit 120. The light shielding member 710 is made of a non-transparent plastic material, for example. This light shielding member 710 is integrally extended from the chassis 113 of the image display device 111A or 111B, or is attached to the chassis 113 of the image forming unit 111A or 111B, or is integrally extended from the frame 10, or is attached to the frame 10. In the shown example, the light shielding member 710 is integrally extended from the chassis 113 of the image forming unit 111A or 111B.

In the display apparatus in Embodiment 9, the light shielding member is provided to an area of the light guide unit where light coming from the image forming unit is input. This light shielding member is for shielding the light guide unit from the outside light. Therefore, even if the operation of the dimmer unit changes the amount of incoming outside light, this does not cause image degradation on the display apparatus with no undesired stray light because no outside light enters the area of the light guide unit where light coming from the image forming unit is input, i.e., the first deflection section 130, in the first place.

Embodiment 10

Embodiment 10 is a modification of Embodiment 9. As shown in a conceptual view of FIG. 26, unlike the display apparatus in Embodiment 9, a display apparatus in Embodiment 10 includes a light shielding member 720 in a portion of the light guide unit 120 on the side not provided with the image forming unit 111A or 111B. Specifically, the light shielding member 720 may be formed with printing on the light guide unit 120 (specifically on the inner surface of the second cover member 162) using a non-transparent ink. Other than that, the display apparatus in Embodiment 10 is in the same structure and configuration as the display apparatus in Embodiment 9, and thus is not described in detail again. The light shielding member 720 in Embodiment 10 may be combined with the light shielding member 710 in Embodiment 9 for use. The light shielding member 720 may be formed on the outer surface of the second cover member 162.

Embodiment 11

Embodiment 11 is also a modification of Embodiment 9. As shown in a conceptual view of FIG. 27 or 28, unlike the display apparatuses in Embodiments 9 and 10, a display apparatus in Embodiment 11 includes a light shielding member 730 in the dimmer unit 700. Specifically, the light shielding member 730 may be formed with printing on the dimmer unit 700 using a non-transparent ink. In the example of FIG. 27, the light shielding member 730 is formed on the outer surface of the first substrate 701 in the dimmer unit 700, and in the example of FIG. 28, the light shielding member 730 is formed on the inner surface of the first substrate 701 in the dimmer unit 700. Other than that, the display apparatus in Embodiment 11 is in the same structure and configuration as the display apparatus in Embodiment 9, and thus is not described in detail again. The light shielding member 730 in Embodiment 11 may be combined with the light shielding member 710 in Embodiment 9 for use, the light shielding member 730 in Embodiment 11 may be combined with the light shielding member 720 in Embodiment 10 for use, or the light shielding member 730 in Embodiment 11 may be combined with the light shielding members 710 and 720 in Embodiments 9 and 10.

Embodiment 12

Embodiment 12 is a modification of Embodiments 6 to 11.

In Embodiments 6 to 11, the light-transmission control material layer 705 is configured by a liquid crystal material layer. On the other hand, as shown in a conceptual view of FIG. 29, in a dimmer unit 700′ in a display apparatus in Embodiment 12, a light-transmission control material layer 705′ is an optical shutter being an inorganic EL material layer. Herein, the inorganic EL material layer is made of tungstic oxide (WO₃). Also in the dimmer unit 700′, first and second substrates 701′ and 703′ are each a transparent glass substrate such as soda lime glass or super white glass, and the second substrate 703′ is made thinner than the first substrate 701′. Specifically, the second substrate 703′ is formed with the thickness of 0.2 mm, and the first substrate 701′ is formed with the thickness of 0.4 mm. Other than that, the display apparatus in Embodiment 12 is in the same structure and configuration as the display apparatuses in Embodiments 6 to 12, and thus is not described in detail again. Herein, the first substrate 701′ in the dimmer unit 700′ is attached to the second cover member 162 using the adhesive 707 similarly to Embodiment 9.

Embodiment 13

Embodiment 13 is a modification of Embodiments 6 to 12, and is specifically about the display apparatus according to the first embodiment of the present disclosure. As shown in a conceptual view of FIG. 30, in a display apparatus in Embodiment 13, a dimmer unit 700″ includes

first and second substrates 701″ and 703″, the first substrate 701″ opposing the light guide unit 120, the second substrate 703″ opposing the first substrate 701″,

electrodes 702″ and 704″ respectively provided to the first and second substrates 701″ and 703″, and

a light-transmission control material layer 705″ sealed between the first and second substrates 701″ and 703″. The first substrate 701″ serves also as the component (specifically the second cover member 162) in the light guide unit 120. That is, the first substrate 701″ and the second cover member 162 are the one specific member, and are for shared use.

As described above, in Embodiment 13, the first substrate 701″ in the dimmer unit 700″ serves also as the component (the second cover member 162) in the light guide unit 120. This reduces the entire weight of the display apparatus so that this does not cause discomfort to a user of the display apparatus.

Other than that, the display apparatus in Embodiment 13 is in the same structure and configuration as the display apparatuses in Embodiments 6 to 12, and thus is not described in detail again. Moreover, the light shielding member in the display apparatus in Embodiment 13 is in the same structure and configuration as the dimmer unit in the display apparatuses in Embodiments 6 to 11, and thus is not described again.

Embodiment 14

Embodiment 14 is a modification of Embodiments 1 to 13.

FIG. 31 is a schematic front view of a head mounted display in Embodiment 14, and FIG. 32 is another schematic front view of the head mounted display in Embodiment 14, i.e., the head mounted display with no frame. FIG. 33 is a schematic top view of the head mounted display in Embodiment 14, and FIG. 34 is a top view of the head mounted display in Embodiment 14 when the head mounted display is mounted on the head portion of the viewer 20. For convenience, FIG. 34 shows only the image display devices, and no frame is shown. In the description below, the image display device 100 is mainly described, but the image display devices 200, 300, and 400 are surely also applicable. In Embodiments 14 and 15, the housing member 160 (and the dimmer unit 700 in some cases) is not shown.

The head mounted display in Embodiment 14 is further provided with a coupling member 170 to couple together the two image display devices 100. The coupling member 170 is attached to a center portion 10C of the frame 10 on the side facing the viewer, i.e., between the viewer 20 and the frame 10, by using a screw (not shown), for example. The frame 10 is positioned between the two eyes 21 of the viewer 20. The projection image of the coupling member 170 is in the projection image of the frame 10. That is, when the head mounted display is viewed from the front of the viewer 20, the coupling member 170 is not visible as is hidden behind the frame 10. In the state that the coupling member 170 couples together the two image display devices 100, specifically, the image forming units 111A and 111B are each housed in the chassis 113, and at each end portion of the coupling member 170, the chassis 113 is attached to be adjustable. The image forming units 111A and 111B are positioned outside of the eyes 21 of the viewer 20. Specifically, such a configuration satisfies

α=0.1×L

β=0.5×L

γ=0.9×L

where α denotes a distance from the attachment center 111A_(C) for one image forming unit 111A to one end portion (one endpiece) 10A of the frame 10, β denotes a distance from the center 170 _(C) of the coupling member 170 to the one end portion (the one endpiece) 10A of the frame 10, γ denotes a distance from the attachment center 111B_(C) for the remaining image forming unit 111B to the one end portion (the one endpiece) 10A of the frame 10, and L denotes a length of the frame 10.

For respectively attaching the image forming units (specifically the image forming units 111A and 111B) to the end portions of the coupling member 170, specifically, three through holes (not shown) are formed to each end portion of the coupling member, and tapped-hole sections (screw sections, not shown) corresponding to these through holes are formed to each of the image forming units 111A and 111B. Thereafter, screws (not shown) are fastened into the hole sections formed to the image forming units 111A and 111B through the through holes. Between each of the screws and each of the whole sections, a spring is inserted in advance. Therefore, by controlling the degree of screw fastening, the image forming units may be adjusted in state of attachment, i.e., adjusted in angle with respect to the coupling member. After such attachment, the screws are each hidden using a lid (not shown). In FIGS. 32 and 36, the coupling member 170 and a coupling member 180 are both shaded for explicit indication thereof. The coupling member 170 is attached to the center portion 10C of the frame 10, which is positioned between the two eyes 21 of the viewer 20. This center portion 10C corresponds to a bridge section of ordinary glasses. On the side of the coupling member 170 facing the viewer 20, a nose pad 10′ is attached. FIGS. 33 and 37 do not show the nose pad 10′. The frame 10 and the coupling member 170 are each made of metal or plastic, and the coupling member 170 is shaped like a bent rod.

In such a head mounted display (HMD) in Embodiment 14, the coupling member 170 couples together the two image display devices 100, and this coupling member 170 is attached to the center portion 10C of the frame 10 that is positioned between the two eyes 21 of the viewer 20. That is, the image display devices 100 are not directly attached to the frame 10. Therefore, the temple sections 13 are extended outward when the viewer 20 wears the frame 10 on his head portion. As a result, even if the frame 10 is deformed, such deformation of the frame 10 does not cause displacement (position change) of the image forming units 111A and 111B, and even if such displacement occurs, the displacement is negligible. Such a configuration thus prevents a change of convergence angle between right and left images without fail. Further, the configuration eliminates having to increase the rigidity of the front section 11 of the frame 10 so that the frame 10 is not increased in weight, the design ability is not impaired, and the cost is not increased. Still further, with the image display devices 100 not directly attached to the eyeglass-shaped frame 10, the frame 10 may be in various designs and colors to meet the viewer's preferences, and the designing of the frame 10 is less restricted and highly flexible. What is more, the coupling member 170 is hidden behind the frame 10 when the head mounted display is viewed from the front of the viewer. This offers the head mounted display with sophistication and refinement of design.

Embodiment 15

Embodiment 15 is a modification of Embodiment 14. FIG. 35 is a schematic front view of a head mounted display in Embodiment 15, and FIG. 36 is another schematic front view of the head mounted display in Embodiment 15, i.e., the head mounted display with no frame. FIG. 37 is a schematic top view of the head mounted display in Embodiment 15.

In the head mounted display in Embodiment 15, unlike in Embodiment 14, the rod-like coupling member 180 does not couple the two image forming units 111A and 111B but the two light guide units 120. Alternatively, the two light guide units 120 may be integrally manufactured, and the resulting integrally-manufactured light guide unit 120 may be provided with the coupling member 180.

Also in the head mounted display in Embodiment 15, using a screw, for example, the coupling member 180 is attached to the center portion 10C of the frame 10 positioned between the two eyes 21 of the viewer 20. The image forming units 111 are positioned outside of the eyes 21 of the viewer 20. The image forming units 111 are each attached to the end portion of the light guide unit 120. When a distance from the center 180 _(C) of the coupling member 180 to an end portion of the frame 10 is β, and when the length of the frame 10 is L, β=0.5×L is satisfied. Note that values of α′ and γ′ in Embodiment 15 are the same as those of α and γ in Embodiment 14.

In Embodiment 15, the frame 10 and the image display devices are in the same structure and configuration as the frame 10 and the image display devices described in Embodiment 14, and thus are not described in detail again. The head mounted display in Embodiment 15 is also substantially in the same structure and configuration as the head mounted display in Embodiment 14 except for the above-mentioned difference, and thus is not described in detail again.

While the present disclosure has been described based on Embodiments in detail, the foregoing description of Embodiments is in all aspects illustrative and not restrictive. The display apparatuses (head mounted displays) and the image display devices in Embodiments are by way of example, and numerous other modifications and variations can be devised therefor. As an example, the light guide plate may be provided with a surface relief hologram (refer to United States Patent Application No. 20040062505A1). In the light guide unit, the diffraction grating element may be a transmissive diffraction grating element, or the first or second deflection section may be a reflective diffraction grating element, and the remaining deflection section may be a transmissive diffraction grating element. Alternatively, the diffraction grating element may be a reflective blazed diffraction grating element. In the display apparatuses in Embodiments 9 and 10, and 12 and 13, in some cases, the dimmer unit is not used but only the light shielding member may be provided.

In Embodiments, the image forming unit 111 or 211 is described to offer image display in a color, e.g., green. The image forming unit 111 or 211 may offer color image display. In this case, the light source may be so configured as to emit light in red, green, and blue, for example. Specifically, the light emitted from red, green, and blue light-emitting elements, i.e., red, green, and blue light, may be mixed and made uniform in luminance using a light pipe to obtain white light.

The dimmer unit may be detachably provided in an area from which the light guide unit emits light. For detachably providing the dimmer unit, the dimmer unit may be attached to the light guide unit using a screw made of transparent plastic, for example. The dimmer unit may be then connected to a control circuit via connectors and wiring lines. This control circuit is for controlling the light transmittance of the dimmer unit, and is provided in the control unit 18 that controls the image forming unit, for example.

In some cases, an optical shutter for use may be configured by application of electrodeposition/dissociation that occurs in response to the reversible oxidation reduction of metal, e.g., silver particles. Specifically, Ag⁺ (silver) and I⁻ (iodine) are dissolved in advance in an organic solvent, and Ag is precipitated by reduction of Ag⁺ through appropriate voltage application to electrodes so that the dimmer unit is reduced in light transmittance. On the other hand, Ag is oxidized and dissolved as Ag⁺, so that the dimming device is increased in light transmittance. Alternatively, in some cases, an optical shutter for use may be configured by utilizing color change of substance that occurs in response to the oxidation reduction of an electrochromic material. Specifically, first and second electrodes are provided, and first and second electrochromic material layers are sandwiched between the first and second electrodes. The first electrochromic material layer is configured by a Prussian blue metal complex, and the second electrochromic material layer is configured by a nickel-substituted Prussian blue metal complex. In other cases, an optical shutter for use may be configured by controlling the light transmittance by electrowetting. Specifically, first and second electrodes are provided, and an insulating first liquid and a conductive second liquid are filled between the first and second electrodes. By voltage application between the first and second electrodes, the interface between the first and second liquids is changed in shape, e.g., from being flat to being bent, thereby controlling the light transmittance.

As the image forming unit or the light source configured by light-emitting elements and a light valve, the following is also possible other than the combination of a backlight emitting white light as a whole and a liquid crystal display including red, green, and blue light-emitting pixels, for example.

As a modification of the image forming unit, an active-matrix image forming unit is also possible as in a conceptual view of FIG. 38, for example, i.e., the image forming unit includes a light-emitting panel in which light-emitting elements 601 being semiconductor laser elements are arranged in a 2D matrix, and the light-emitting elements 601 are each controlled to emit/not to emit light. Such control allows direct perception of light emission in the light-emitting elements 601, whereby images are displayed. The light emitted from this image forming unit is input to the light guide plate 121 via the collimator optical system 112. Also in the below, the light-emitting elements are semiconductor laser elements.

A color-display image forming unit in a conceptual view of FIG. 39 is also possible. This image forming unit includes

(α) a red light-emitting panel 611R in which red light-emitting elements 601R are arranged in a 2D matrix, the red light-emitting elements 601R emitting red light,

(β) a green light-emitting panel 611G in which green light-emitting elements 601G are arranged in a 2D matrix, the green light-emitting elements 601G emitting green light,

(γ) a blue light-emitting panel 611B in which blue light-emitting elements 601B are arranged in a 2D matrix, the blue light-emitting elements 601B emitting blue light, and

(δ) a section configured to collectively direct the light emitted from the red, green, and blue light-emitting panels 611R, 611G, and 611B to a single optical path, e.g., dichroic prism 603.

This color-display image forming unit controls light-emission/no light-emission of the red, green, and blue light-emitting elements 601R, 601G, and 601B. The light emitted from this image forming unit is also input to the light guide plate 121 via the collimator optical system 112.

Herein, a reference numeral 612 denotes a micro lens for gathering the light coming from the light-emitting elements.

FIG. 40 is a conceptual view of an image forming unit configured by the light-emitting panels 611R, 611G, 611B, and others in which the light-emitting elements 601R, 601G, and 601B are each arranged in a 2D matrix. The light emitted from the light-emitting panels 611R, 611G, and 611B is controlled by light-pass control units 604R, 604G, and 604B in terms of light-pass/no light-pass. The light then enters the dichroic prism 603, is collectively directed to a single optical path, and is then input to the light guide plate 121 via the collimator optical system 112.

FIG. 41 is a conceptual view of the image forming unit configured by the light-emitting panels 611R, 611G, 611B, and others in which the light-emitting elements 601R, 601G, and 601B are each arranged in a 2D matrix. The light emitted from the light-emitting panels 611R, 611G, and 611B enters the dichroic prism 603, and is collectively directed to a single optical path. The light from the dichroic prism 603 is then controlled by the light-pass control unit 604 in terms of light-pass/no light-pass, and is input to the light guide plate 121 via the collimator optical system 112.

An image forming unit of FIG. 42 is also possible. This image forming unit includes the light-emitting elements 601R emitting red light, a light-pass control unit being a light valve for controlling light-pass/no light-pass of the light emitted from the red light-emitting elements 601R, e.g., liquid crystal display 604R, the light-emitting elements 601G emitting green light, a light-pass control unit being a light valve for controlling light-pass/no light-pass of the light emitted from the green light-emitting elements 601G, e.g., liquid crystal display 604G, the light-emitting elements 601B emitting blue light, and a light-pass control unit being a light valve for controlling light-pass/no light-pass of the light emitted from the blue light-emitting elements 601B, e.g., liquid crystal display 604B. The image forming unit also includes a light directing member 602 configured to guide the light emitted from the light-emitting elements 601R, 601G, and 601B, and a section configured to collectively direct the light to a single optical path, e.g., dichroic prism 603. The light emitted from the dichroic prism 603 is input to the light guide plate 121 via the collimator optical system 112.

The present disclosure may be also in the following structures.

[A01] (Image Display Device)

An image display device, including:

(A) an image forming unit; and

(B) a light guide unit, the light guide unit including

-   -   a light guide plate configured to guide light of an image formed         in the image forming unit, and     -   a housing member configured to house the light guide plate, the         housing member including         -   a first cover member,         -   a second cover member attached to the first cover member,             and         -   an attachment member configured to attach the light guide             plate to a housing unit that is surrounded by the first             cover member and the second cover member.

[A02] The Image Display Device According to [A01], in Which

the attachment member is made of a thermal insulation material.

[A03] The Image Display Device According to [A02], in Which

the attachment member has a thermal conductivity smaller than a thermal conductivity of each of the light guide plate, the first cover member, and the second cover member.

[A04] The Image Display Device According to [A01], in Which

the attachment member is made of a buffer material.

[A05] The Image Display Device According to [A04], in Which

the attachment member has an elastic modulus smaller than an elastic modulus of the light guide plate.

[A06] The Image Display Device According to Any One of [A01] to [A05], in Which

the light guide plate is attached to the first cover member by the attachment member.

[A07] The Image Display Device According to Any One of [A01] to [A06], in Which

a gap is provided between the light guide plate and the first cover member, and

a gap is provided between the light guide plate and the second cover member.

[A08] The Image Display Device According to [A07], in Which

air is present in the gaps.

[A09] The Image Display Device According to [A08], in which

at least one of the first cover member and the second cover member has an opening.

[A10] The Image Display Device According to [A07], in Which

the gaps are each filled with inert gas.

[A11] The Image Display Device According to [A07], in Which

the gaps are each at a reduced pressure.

[A12] The Image Display Device According to Any One of [A01] to [A06], in Which

a resin layer is provided between the light guide plate and the first cover member, and

a resin layer is provided between the light guide plate and the second cover member.

[A13] The Image Display Device According to [A12], in Which

the resin layer has a thermal conductivity smaller than a thermal conductivity of each of the light guide plate, the first cover member, and the second cover member.

[A14] The Image Display Device According to Any One of [A01] to [A13], in Which

the first cover member and the second cover member are each made of a material through which light passes.

[A15] The Image Display Device According to Any One of [A01] to [A14], in Which

an ultraviolet ray protective layer is provided to an outer surface of the cover member on a side to which outside light is input.

[A16] The Image Display Device According to Any One of [A01] to [A15], in Which

a dimmer unit is attached to the cover member on a side to which outside light is input.

[B01] (Light Guide Unit)

A light guide unit, including:

a light guide plate; and

a housing member configured to house the light guide plate, the housing member including

-   -   a first cover member,     -   a second cover member attached to the first cover member, and     -   an attachment member configured to attach the light guide plate         to a housing unit that is surrounded by the first cover member         and the second cover member.

[B02] The Light Guide Unit According to [B01], in Which

the attachment member is made of a thermal insulation material.

[B03] The Light Guide Unit According to [B02], in Which

the attachment member has a thermal conductivity smaller than a thermal conductivity of each of the light guide plate, the first cover member, and the second cover member.

[B04] The Light Guide Unit According to [B01], in Which

the attachment member is made of a buffer material.

[B05] The Light Guide Unit According to [B04], in Which

the attachment member has an elastic modulus smaller than an elastic modulus of the light guide plate.

[B06] The Light Guide Unit According to Any One of [B01] to [B05], in Which

the light guide plate is attached to the first cover member by the attachment member.

[B07] The Light Guide Unit According to Any One of [B01] to [B06], in Which

a gap is provided between the light guide plate and the first cover member, and

a gap is provided between the light guide plate and the second cover member.

[B08] The Image Display Device According to [B07], in Which

air is present in the gaps.

[B09] The Light Guide Unit According to [B08], in Which

at least one of the first cover member and the second cover member has an opening.

[B10] The Light Guide Unit According to [B07], in Which

the gaps are each filled with inert gas.

[B11] The Light Guide Unit According to [B07], in Which

the gaps are each at a reduced pressure.

[B12] The Light Guide Unit According to Any One of [B01] to [B06], in Which

a resin layer is provided between the light guide plate and the first cover member, and

a resin layer is provided between the light guide plate and the second cover member.

[B13] The Light Guide Unit According to [B12], in Which

the resin layer has a thermal conductivity smaller than a thermal conductivity of each of the light guide plate, the first cover member, and the second cover member.

[B14] The Light Guide Unit According to Any One of [B01] to [B13], in Which

the first cover member and the second cover member are each made of a material through which light passes.

[B15] The Light Guide Unit According to Any One of [B01] to [B14], in Which

an ultraviolet ray protective layer is provided to an outer surface of the cover member on a side to which outside light is input.

[B16] The Light Guide Unit According to Any One of [B01] to [B15], in Which

a dimmer unit is attached to the cover member on a side to which outside light is input.

[C01] (Display Apparatus)

A display apparatus, including:

(1) a frame configured to be mounted on a viewer's head portion; and

(2) an image display device attached to the frame, the image display device including

-   -   (A) an image forming unit, and     -   (B) a light guide unit, the light guide unit including         -   a light guide plate configured to guide light of an image             formed in the image forming unit, and         -   a housing member configured to house the light guide plate,             the housing member including             -   a first cover member,             -   a second cover member attached to the first cover                 member, and             -   an attachment member configured to attach the light                 guide plate to a housing unit that is surrounded by the                 first cover member and the second cover member.

[C02] (Display Apparatus)

A display apparatus, including:

(1) a frame configured to be mounted on a viewer's head portion; and

(2) an image display device attached to the frame, the image display device including

-   -   (A) an image forming unit, and     -   (B) a light guide unit, the light guide unit including         -   a light guide plate configured to guide light of an image             formed in the image forming unit, and         -   a housing member configured to house the light guide plate,             the housing member including the housing member according to             any one of [B01] to [B16].

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 

What is claimed is:
 1. An image display device, comprising: an image forming unit; and a light guide unit, the light guide unit including a light guide plate configured to guide light of an image formed in the image forming unit, and a housing member configured to house the light guide plate, the housing member including a first cover member, a second cover member attached to the first cover member, and an attachment member configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member.
 2. The image display device according to claim 1, wherein the attachment member is made of a thermal insulation material.
 3. The image display device according to claim 2, wherein the attachment member has a thermal conductivity smaller than a thermal conductivity of each of the light guide plate, the first cover member, and the second cover member.
 4. The image display device according to claim 1, wherein the attachment member is made of a buffer material.
 5. The image display device according to claim 4, wherein the attachment member has an elastic modulus smaller than an elastic modulus of the light guide plate.
 6. The image display device according to claim 1, wherein the light guide plate is attached to the first cover member by the attachment member.
 7. The image display device according to claim 1, wherein a gap is provided between the light guide plate and the first cover member, and a gap is provided between the light guide plate and the second cover member.
 8. The image display device according to claim 7, wherein air is present in the gaps.
 9. The image display device according to claim 8, wherein at least one of the first cover member and the second cover member has an opening.
 10. The image display device according to claim 7, wherein the gaps are each filled with inert gas.
 11. The image display device according to claim 7, wherein the gaps are each at a reduced pressure.
 12. The image display device according to claim 1, wherein a resin layer is provided between the light guide plate and the first cover member, and a resin layer is provided between the light guide plate and the second cover member.
 13. The image display device according to claim 12, wherein the resin layer has a thermal conductivity smaller than a thermal conductivity of each of the light guide plate, the first cover member, and the second cover member.
 14. The image display device according to claim 1, wherein the first cover member and the second cover member are each made of a material through which light passes.
 15. The image display device according to claim 1, wherein an ultraviolet ray protective layer is provided to an outer surface of the cover member on a side to which outside light is input.
 16. The image display device according to claim 1, wherein a dimmer unit is attached to the cover member on a side to which outside light is input.
 17. A light guide unit, comprising: a light guide plate; and a housing member configured to house the light guide plate, the housing member including a first cover member, a second cover member attached to the first cover member, and an attachment member configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member.
 18. A display apparatus, comprising: a frame configured to be mounted on a viewer's head portion; and an image display device attached to the frame, the image display device including an image forming unit, and a light guide unit, the light guide unit including a light guide plate configured to guide light of an image formed in the image forming unit, and a housing member configured to house the light guide plate, the housing member including a first cover member, a second cover member attached to the first cover member, and an attachment member configured to attach the light guide plate to a housing unit that is surrounded by the first cover member and the second cover member. 